Geophysical evaluation methods for buried hill reservoirs in the Jiyang superdepression of the Bohai Bay basin, eastern China

The Jiyang superdepression is one of the richest hydrocarbon accumulations in the Bohai Bay basin, eastern China. Comprehensive seismic methods have been used in buried hill exploration in Jiyang to describe these fractured reservoirs better. Accurate seismic stratigraphic demarcation and variable-velocity mapping were applied to reveal the inner structure of the buried hills and determine the nature of the structural traps more precisely. Based on the analysis of rock properties and the characteristics of well-developed buried hill reservoirs, we have successfully linked the geology and seismic response by applying seismic forward technology. Log-constrained inversion, absorption coefficient analysis and tectonic forward-inversion with FMI loggings were applied to analyse and evaluate the buried hill reservoirs and gave satisfying results. The reservoir prediction was successful, which confirmed that the comprehensive utilization of these methods can be helpful in the exploration of buried hill reservoirs.

裂缝储层预测技术应用研究

In practice,many fracture reservoir was found,which has giant potential for exporation. For example,in limestone fracture reservoir,igneous rock fracture reservoir and shale fracture reservoir ,there are high yield oil wells found. The fracture reservoir has strong anisotropy and is very difficult to explore and produce.Since 1990’s,the techniques that use structure information and P-WAVE seismic attributes to detect fracture developed very rapidly,include stress and strain analysis,using amplitude,interval velocity,time-difference,azimuthal AVO analysis etc. Based on research and develop these advanced techniques of fracture detect,this paper selected two typical fracture reservoir as target area,according to the characters of research area,selected different techniques to pridect the fracture azimuth and density of target,and at last ,confirmed the favored area. This paper includes six parts:the first chapter mainly addresses the domestic and international research actuality about the fracture prediction and the evolement in ShengLi oil field,then according to the temporal exploration requirement,a research route was established; Based on the close relationship between structural fracture and the geotectonic movement and the procedure of rock distortion，the second chapter research the structural fracture predicting technique which is realized by computing the strain in every geotectonic movement ,which is by use of the forward and inversion of the growing history of structure; The third chapter discussed many kind of traditional techniques for fracture reservoir prediction,and point out their disadvantages.then research and develop the coherence volume computing technique which can distinguish from faults,the seismic wave absorbing technique,and other fracture predicting technique which is by use of seismic attributes ,such as azimuthal AVO FVO etc; The fourth chapter first establish the geological and petrophysical model by use of the existed log and drill well information, then research the variation of amplitude and seismic wave which is caused by fractures.based on it , the fracture predicting technique which is by use of variation of azimuthal impedance is researched;The fifth chapter is a case study,it selects shale fracture reservoir in LuoJia area as target,selects several kind of techniques to apply ,at last ,the fracture distribution of target reservoir and favored area were gotten;the sixth chapter is another case study,it selects limestone fracture reservoir in BoShen6 buried hill as target,selects several kind of techniques to apply,similarly favored area were gotten. Based on deeply research and development of the new techniques for fracture reservoir exploration, This paper selects two fracture reservoirs the most typical in ShengLi as targets to be applied ,good results show up a good application way ,which can be used for reference for future fracture exploration,and it can bring materially economic and social benefit.

裂缝性油气藏储层预测方法研究

In this paper, based on the E & P situation in the oilfield and the theory of geophysical exploration, a series researches are conducted on fracture reservoir prediction technology in general，and it especially focus on some difficult points. The technological series which integrated amplitude preserved data processing、interpretation and its comprehensive application research as a whole were developed and this new method can be applied to the other similar oilfield exploration and development. The contents and results in this paper are listed as follows: 1. An overview was given on the status and development of fracture reservoir estimation technique, compare and analyze those geophysical prediction methods. This will be very helpful to the similar reservoir researches. 2. Analyze and conclude the characters of geologies and well logging response of burial hills fracture reservoir, those conclusions are used to steer the geophysical research and get satisfying results. 3. Forward modeling anisotropy seismic response of fracture reservoir. Quantitatively describe the azimuthal amplitude variation. Amplitude ellipse at each incidence angle is used to identify the fracture orientation. 4. Numerical simulation of structure stress based on finite difference method is carried out. Quantitatively describe and analyze the direction and intensity of fracture. 5. Conventional attributes extraction of amplitude preserved seismic data、attributes with different azimuthal angle and different offset are used to determine the relationship between the results and fracture distribution. 6. With spectrum decomposition method based on wavelet transform， the author disclose the reservoir distribution in space. It is a powerful tool to display its anisotropy. 7. Integrated seismic wave impendence、elastic impendence、spectrum decomposition、attribute extraction、fracture analysis result as a whole to identify and evaluate the fracture reservoir. An optimum workflow is constructed. It is used to practical oil&gas production and good results are obtained. This can indicate the wide foreground of this technique series.

天然气藏地震识别技术研究

The Research of Seismic Recognition Techniques for Gas Reservoir Shang Yong_sheng(Geophysics) Directed by Yang Chang-chun Abstract Gas reservior is one of the most important nature resources. Someone forecast that the output will exceed crude oil in 2015 and become the largest energy source. Recently,more and more gas reservior are discovered as the oil field and gas filed exploration go deep into development. Although the gas proved reserves rise greatly the explorative degree of natural gas resource in our country is still very low. The potential of gas exploration is very great and our task is so hard. How to recognise and discover new gas reservoir is the first task based on the great gas reservior resources foreground. the gas reservior in different oil and gas field have its special gas generation, reservoiring, physical property conditions. However,it may have the same geophysical characters. So,it is very important to analyse, research, summarizing the geophysical characters of the gas reservior and make use of the characters to identify the gas layer effectively. This paper start with modeling,and it discuss the geophysical characters of the gas reservior response. It analyse the seismical wave characters of the gas reservoir. Furthermore, it summarize the method of using the seismica profile to identify the gas reservior directly. The paper discuss the research of extracting diffraction wave for mass diffraction wave grow at the edge of the gas reservoir at the seismic section. Making use of the technique of extracting diffraction wave to identify the gas reservior is the first experiment of the gas reservoir prediction technique. The avo technology is a new geophysical method. From the pre-stack analysis, this paper discuss the technique of using the rich information to identify the gas reservoir. Based on the case study of the Qidam basin and the Hailaer basin it discuss the method of predicating gas reservoir using pre-stack information. It include pre-stack amplitude preserve process, AVO modeling, fluid replacement technique, AVO analysis and interpretation technique. The paper summarize a gas reservoir prediction procedure focusing on the pre-stack information. The seismic wave will cause great attenuation when it pass through the gas layer and the high frequency component loss. This paper discuss the technique of extracting seismic attributes to represent the attenuation degree of seismica wave. Based on the attenuation attributes,it does the research of the gas reservor identification and prediction. At last,the paper discuss the method of calculating the azimuthal anisotropy to predict the fracture reservoir. Keyword: gas reservoir, diffraction wave, AVO, attenuation attribute,fracture prediction

沾化凹陷泥质岩油气藏成藏特征研究

Mudstone reservoir is a subtle reservoir with extremely inhomogeneous, whose formation is greatly related to the existence of fracture. For this kind of reservoir, mudstone is oil source rock, cover rock and reservoir strata, reservoir type is various, attitude of oil layer changes greatly, and the distribution of oil and gas is different from igneous or clastic rock reservoir as well as from carbonate reservoir of self-producing and self-containing of oil and gas. No mature experience has been obtained in the description, exploration and development of the reservoir by far. Taking Zhanhua depression as an example, we studied in this thesis the tectonic evolution, deposit characteristics, diagenesis, hydrocarbon formation, abnormal formation pressure, forming of fissure in mudstone reservoir, etc. on the basis of core analysis, physical simulation, numerical simulation, integrated study of well logging and geophysical data, and systematically analyzed the developing and distributing of mudstone fissure reservoir and set up a geological model for the formation of mudstone fissure reservoir, and predicted possible fractural zone in studied area. Mudstone reservoir mainly distributed on the thrown side of sedimentary fault along the sloping area of the petroleum generatiion depression in Zhanhua depression. Growing fault controlled subsidence and sedimentation. Both the rate of subsidence and thickness of mudstone are great on the thrown side of growing fault, which result in the formation of surpressure in the area. The unlocking of fault which leads to the pressure discharges and the upward conduct of below stratum, also makes for the surpressure in mudstone. In Zhanhua depression, mudstone reservior mainly developed in sub-compacted stratum in the third segment of Shahejie formation, which is the best oil source rock because of its wide spread in distribution, great in thickness, and rich in organic matter, and rock types of which are oil source mudstone and shale of deep water or semi-deep water sediment in lacustrine facies. It revealed from core analysis that the stratum is rich in limestone, and consists of lamina of dark mudstone and that of light grey limestone alternately, such rock assemblage is in favor of high pressure and fracture in the process of hydrocarbon generation. Fracture of mudstone in the third segment of Shahejie formation was divided into structure fracture, hydrocarbon generation fracture and compound fracture and six secondary types of fracture for the fist time according to the cause of their formation in the thesis. Structural fracture is formed by tectonic movement such as fold or fault, which develops mainly near the faults, especially in the protrude area and the edge of faults, such fracture has obvious directivity, and tend to have more width and extension in length and obvious direction, and was developed periodically, discontinuously in time and successively as the result of multi-tectonic movement in studied area. Hydrocarbon generation fracture was formed in the process of hydrocarbon generation, the fracture is numerous in number and extensively in distribution, but the scale of it is always small and belongs to microfracture. The compound fracture is the result of both tectonic movement and hydrocarbon forming process. The combination of above fractures in time and space forms the three dimension reservoir space network of mudstone, which satellites with abnormal pressure zone in plane distribution and relates to sedimentary faces, rock combination, organic content, structural evolution, and high pressure, etc.. In Zhanhua depression, the mudstone of third segment in shahejie formation corresponds with a set of seismic reflection with better continuous. When mudstone containing oil and gas of abnormal high pressure, the seismic waveform would change as a result of absorb of oil and gas to the high-frequency composition of seismic reflection, and decrease of seismic reflection frequency resulted from the breakage of mudstone structure. The author solved the problem of mudstone reservoir predicting to some degree through the use of coherent data analysis in Zhanhua depression. Numerical modeling of basin has been used to simulate the ancient liquid pressure field in Zhanhua depression, to quantitative analysis the main controlling factor (such as uncompaction, tectonic movement, hydrocarbon generation) to surpressure in mudstone. Combined with factual geologic information and references, we analyzed the characteristic of basin evolution and factors influence the pressure field, and employed numerical modeling of liquid pressure evolution in 1-D and 2-D section, modeled and analyzed the forming and evolution of pressure in plane for main position in different periods, and made a conclusion that the main factors for surpressure in studied area are tectonic movement, uncompaction and hydrocarbon generation process. In Zhanhua depression, the valid fracture zone in mudstone was mainly formed in the last stage of Dongying movement, the mudstone in the third segment of Shahejie formation turn into fastigium for oil generation and migration in Guantao stage, and oil and gas were preserved since the end of the stage. Tectonic movement was weak after oil and gas to be preserved, and such made for the preserve of oil and gas. The forming of fractured mudstone reservoir can be divided into four different stages, i.e. deposition of muddy oil source rock, draining off water by compacting to producing hydrocarbon, forming of valid fracture and collecting of oil, forming of fracture reservoir. Combined with other regional geologic information, we predicted four prior mudstone fracture reservoirs, which measured 18km2 in area and 1200 X 104t in geological reserves.

Effects of Fracture Seepage on the Stability of Landslide during Reservoir Water Level Fluctuation

The hydraulic conductivity function of fractures is a key scientific question to describe and reveal the process and the role of water seepage reasonably. In this paper, the generation technology of random fracture network and the latest numerical computation method for equivalent permeability tensor of fracture network are applied to analyze the landslide located at Wangjiayuanzi in Wanzhou District of Chongqing by simulating the changes of the seepage field caused by the running of the Three Gorges Reservoir. The influences of the fracture seepage on the seepage field and stability of the landslide were discussed with emphasis. The results show that the fractures existing in the soil increase the permeability coefficient of the landslide body and reduce the delay time of the underground water level in the landslide which fluctuates relative to the water level of reservoir，that causes the safe coefficient of the slope changes more gently than that of the same slope without fractures. It means, if only water level fluctuating condition is concerned, the fractures existing in the soil plays a positive role to the stability of slopes.

Diagenesis of a light, tight-oil chert reservoir at the Ediacaran/Cambrian boundary, Sultanate of Oman

The Al Shomou Silicilyte Member (Athel Formation) in the South Oman Salt Basin shares many of the characteristics of a light, tight-oil (LTO) reservoir: it is a prolifi c source rock mature for light oil, it produces light oil from a very tight matrix and reservoir, and hydraulic fracking technology is required to produce the oil. What is intriguing about the Al Shomou Silicilyte, and different from other LTO reservoirs, is its position related to the Precambrian/Cambrian Boundary (PCB) and the fact that it is a ‘laminated chert‘ rather than a shale. In an integrated diagenetic study we applied microstructural analyses (SEM, BSE) combined with state-of-the-art stable isotope and trace element analysis of the silicilyte matrix and fractures. Fluid inclusion microthermometry was applied to record the salinity and minimum trapping temperatures. The microstructural investigations reveal a fi ne lamination of the silicilyte matrix with a mean lamina thickness of ca. 20 μm consisting of predominantly organic matter-rich and fi nely crystalline quartz-rich layers, respectively. Authigenic, micron-sized idiomorphic quartz crystals are the main matrix components of the silicilyte. Other diagenetic phases are pyrite, apatite, dolomite, magnesite and barite cements. Porosity values based on neutron density logs and core plug data indicate porosity in the silicilyte ranges from less than 2% to almost to 40%. The majority of the pore space in the silicilyte is related to (primary) inter-crystalline pores, with locally important oversized secondary pores. Pore casts of the silica matrix show that pores are extremely irregular in three dimensions, and are generally interconnected by a complex web or meshwork of fi ne elongate pore throats. Mercury injection capillary data are in line with the microstructural observations suggesting two populations of pore throats, with an effective average modal diameter of 0.4 μm. The acquired geochemical data support the interpretation that the primary source of the silica is the ambient seawater rather than hydrothermal or biogenic. A maximum temperature of ca. 45°C for the formation of microcrystalline quartz in the silicilyte is good evidence that the lithifi cation and crystallization of quartz occurred in the fi rst 5 Ma after deposition. Several phases of brittle fracturing and mineralization occurred in response to salt tectonics during burial. The sequences of fracture-fi lling mineral phases (dolomite - layered chalcedony – quartz – apatite - magnesite I+II - barite – halite) indicates a complex fl uid evolution after silicilyte lithifi cation. Primary, all-liquid fl uid inclusions in the fracturefi lling quartz are good evidence of growth beginning at low temperatures, i.e. ≤ 50ºC. Continuous precipitation during increasing temperature and burial is documented by primary two-phase fl uid inclusions in quartz cements that show brines at 50°C and fi rst hydrocarbons at ca. 70°C. The absolute timing of each mineral phase can be constrained based on U-Pb geochronometry, and basin modelling. Secondary fl uid inclusions in quartz, magnesite and barite indicate reactivation of the fracture system after peak burial temperature during the major cooling event, i.e. uplift, between 450 and 310 Ma. A number of fi rst-order trends in porosity and reservoir-quality distribution are observed which are strongly related to the diagenetic and fl uid history of the reservoir: the early in-situ generation of hydrocarbons and overpressure development arrests diagenesis and preserves matrix porosity. Chemical compaction by pressure dissolution in the fl ank areas could be a valid hypothesis to explain the porosity variations in the silicilitye slabs resulting in lower porosity and poorer connectivity on the fl anks of the reservoir. Most of the hydrocarbon storage and production comes from intervals characterized by Amthor et al. 114488 preserved micropores, not hydrocarbon storage in a fracture system. The absence of oil expulsion results in present-day high oil saturations. The main diagenetic modifi cations of the silicilyte occurred and were completed relatively early in its history, i.e. before 300 Ma. An instrumental factor for preserving matrix porosity is the diffi culty for a given slab to evacuate all the fl uids (water and hydrocarbons), or in other words, the very good sealing capacity of the salt embedding the slab.

Assessing Fracture Connectivity using Stable and Clumped Isotope Geochemistry of Calcite Cements

Understanding flow path connectivity within a geothermal reservoir is a critical component for efficiently producing sustained flow rates of hot fluids from the subsurface. I present a new approach for characterizing subsurface fracture connectivity that combines petrographic and cold cathodoluminescence (CL) microscopy with stable isotope analysis (δ18O and δ13C) and clumped isotope (Δ47) thermometry of fracture-filling calcite cements from a geothermal reservoir in northern Nevada. Calcite cement samples were derived from both drill cuttings and core samples taken at various depths from wells within the geothermal field. CL microscopy of some fracture filling cements shows banding parallel to the fracture walls as well as brecciation, indicating that the cements are related to fracture opening and fault slip. Variations in trace element composition indicated by the luminescence patterns reflect variations in the composition and source of fluids moving through the fractures as they opened episodically. Calcite δ13C and δ18O results also show significant variation among the sampled cements, reflecting multiple generations of fluids and fracture connectivity. Clumped isotope analyses performed on a subset of the cements analyzed for conventional δ18O and δ13C mostly show calcite growth temperatures around 150°C—above the current ambient rock temperature, which indicates a common temperature trend for the geothermal reservoir. However, calcite cements sampled along faults located within the well field showed both cold (18.7°C) and hot (226.1°C) temperatures. The anomalously cool temperature found along the fault, using estimates from clumped isotope thermometry, suggests a possible connection to surface waters for the geothermal source fluids for this system. This information may indicate that some of the faults within the well field are transporting meteoric water from the surface to be heated at depth, which then is circulated through a complex network of fractures and other faults.

Large-scale dynamic hydrofracturing, healing and fracture network characterization

Permeability of a rock is a dynamic property that varies spatially and temporally. Fractures provide the most efficient channels for fluid flow and thus directly contribute to the permeability of the system. Fractures usually form as a result of a combination of tectonic stresses, gravity (i.e. lithostatic pressure) and fluid pressures. High pressure gradients alone can cause fracturing, the process which is termed as hydrofracturing that can determine caprock (seal) stability or reservoir integrity. Fluids also transport mass and heat, and are responsible for the formation of veins by precipitating minerals within open fractures. Veining (healing) thus directly influences the rock’s permeability. Upon deformation these closed factures (veins) can refracture and the cycle starts again. This fracturing-healing-refacturing cycle is a fundamental part in studying the deformation dynamics and permeability evolution of rock systems. This is generally accompanied by fracture network characterization focusing on network topology that determines network connectivity. Fracture characterization allows to acquire quantitative and qualitative data on fractures and forms an important part of reservoir modeling. This thesis highlights the importance of fracture-healing and veins’ mechanical properties on the deformation dynamics. It shows that permeability varies spatially and temporally, and that healed systems (veined rocks) should not be treated as fractured systems (rocks without veins). Field observations also demonstrate the influence of contrasting mechanical properties, in addition to the complexities of vein microstructures that can form in low-porosity and permeability layered sequences. The thesis also presents graph theory as a characterization method to obtain statistical measures on evolving network connectivity. It also proposes what measures a good reservoir should have to exhibit potentially large permeability and robustness against healing. The results presented in the thesis can have applications for hydrocarbon and geothermal reservoir exploration, mining industry, underground waste disposal, CO2 injection or groundwater modeling.

Simulation of the nutrient supply in fracture healing

The healing process for bone fractures is sensitive to mechanical stability and blood supply at the fracture site. Most currently available mechanobiological algorithms of bone healing are based solely on mechanical stimuli, while the explicit analysis of revascularization and its influences on the healing process have not been thoroughly investigated in the literature. In this paper, revascularization was described by two separate processes: angiogenesis and nutrition supply. The mathematical models for angiogenesis and nutrition supply have been proposed and integrated into an existing fuzzy algorithm of fracture healing. The computational algorithm of fracture healing, consisting of stress analysis, analyses of angiogenesis and nutrient supply, and tissue differentiation, has been tested on and compared with animal experimental results published previously. The simulation results showed that, for a small and medium-sized fracture gap, the nutrient supply is sufficient for bone healing, for a large fracture gap, non-union may be induced either by deficient nutrient supply or inadequate mechanical conditions. The comparisons with experimental results demonstrated that the improved computational algorithm is able to simulate a broad spectrum of fracture healing cases and to predict and explain delayed unions and non-union induced by large gap sizes and different mechanical conditions. The new algorithm will allow the simulation of more realistic clinical fracture healing cases with various fracture gaps and geometries and may be helpful to optimise implants and methods for fracture fixation.

Modelling the effects of bone fragment contact in fracture healing

The fracture healing process is modulated by the mechanical environment created by imposed loads and motion between the bone fragments. Contact between the fragments obviously results in a significantly different stress and strain environment to a uniform fracture gap containing only soft tissue (e.g. haematoma). The assumption of the latter in existing computational models of the healing process will hence exaggerate the inter-fragmentary strain in many clinically-relevant cases. To address this issue, we introduce the concept of a contact zone that represents a variable degree of contact between cortices by the relative proportions of bone and soft tissue present. This is introduced as an initial condition in a two-dimensional iterative finite element model of a healing tibial fracture, in which material properties are defined by the volume fractions of each tissue present. The algorithm governing the formation of cartilage and bone in the fracture callus uses fuzzy logic rules based on strain energy density resulting from axial compression. The model predicts that increasing the degree of initial bone contact reduces the amount of callus formed (periosteal callus thickness 3.1mm without contact, down to 0.5mm with 10% bone in contact zone). This is consistent with the greater effective stiffness in the contact zone and hence, a smaller inter-fragmentary strain. These results demonstrate that the contact zone strategy reasonably simulates the differences in the healing sequence resulting from the closeness of reduction.

In search of a hidden long-term isolated sub-chondritic 142Nd/144Nd reservoir in the deep mantle : implications for the Nd isotope systematics of the Earth

Here we search for evidence of the existence of a sub-chondritic 142Nd/144Nd reservoir that balances the Nd isotope chemistry of the Earth relative to chondrites. If present, it may reside in the source region of deeply sourced mantle plume material. We suggest that lavas from Hawai’i with coupled elevations in 186Os/188Os and 187Os/188Os, from Iceland that represent mixing of upper mantle and lower mantle components, and from Gough with sub-chondritic 143Nd/144Nd and high 207Pb/206Pb, are favorable samples that could reflect mantle sources that have interacted with an Early-Enriched Reservoir (EER) with sub-chondritic 142Nd/144Nd. High-precision Nd isotope analyses of basalts from Hawai’i, Iceland and Gough demonstrate no discernable 142Nd/144Nd deviation from terrestrial standards. These data are consistent with previous high-precision Nd isotope analysis of recent mantle-derived samples and demonstrate that no mantle-derived material to date provides evidence for the existence of an EER in the mantle. We then evaluate mass balance in the Earth with respect to both 142Nd/144Nd and 143Nd/144Nd. The Nd isotope systematics of EERs are modeled for different sizes and timing of formation relative to ε143Nd estimates of the reservoirs in the μ142Nd = 0 Earth, where μ142Nd is ((measured 142Nd/144Nd/terrestrial standard 142Nd/144Nd)−1 * 10−6) and the μ142Nd = 0 Earth is the proportion of the silicate Earth with 142Nd/144Nd indistinguishable from the terrestrial standard. The models indicate that it is not possible to balance the Earth with respect to both 142Nd/144Nd and 143Nd/144Nd unless the μ142Nd = 0 Earth has a ε143Nd within error of the present-day Depleted Mid-ocean ridge basalt Mantle source (DMM). The 4567 Myr age 142Nd–143Nd isochron for the Earth intersects μ142Nd = 0 at ε143Nd of +8 ± 2 providing a minimum ε143Nd for the μ142Nd = 0 Earth. The high ε143Nd of the μ142Nd = 0 Earth is confirmed by the Nd isotope systematics of Archean mantle-derived rocks that consistently have positive ε143Nd. If the EER formed early after solar system formation (0–70 Ma) continental crust and DMM can be complementary reservoirs with respect to Nd isotopes, with no requirement for significant additional reservoirs. If the EER formed after 70 Ma then the μ142Nd = 0 Earth must have a bulk ε143Nd more radiogenic than DMM and additional high ε143Nd material is required to balance the Nd isotope systematics of the Earth.