Lithologic Reservoirs

There are two measuring methods of stress sensibility of reservoir rocks: constant-pore-pressure changing-confining-pressure procedure and constant-confining-pressure changing-pore-pressure procedure. Constant-pore-pressure changing-confining-pressure procedure is simple and easy in operation, while constant-confining-pressurechanging-pore-pressure procedure is complex and difficult in operation. The pore-pressure stress-sensibility curve by constant-confining-pressure changing-pore-pressure procedure can be used to evaluate the stress sensibility directly.However, the confining-pressure stress-sensibility curve by constant-pore-pressure changing-confining-pressure proce-dure must be transformed into pore-pressure stress-sensibility curve through effective stress of rocks for evaluation ofstress sensibility. The evaluation results of the both methods are same. The constant-confining-pressure changing-pore-pressure procedure does not have any advantage and should be abandoned. The stress sensitivity of reservoir rocks is only related with stress sensitivity coefficient and porosity and not related with pressure values of experiments, so the experimental pressure should not be raised to quite high level in order to avoid high pressure risks.

Gas content calculation model of shale gas reservoir

Zhang Zuoqing,Sun Jianmeng,Gong Jingsong,Xia Zhilin

2015, Vol.27(6): 5–14 Abstract ( 485 ) PDF (856 KB) ( 591 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.002

Shale gas is important unconventional resource. Based on the experimental isotherm adsorption data, the factors affecting the adsorption of shale were analyzed and the calculation model of shale adsorbed gas content was established by KIM equation. Through the establishment of shale rock physics model, the pore system was divided and a shale rock conductivity model was set up, and shale free gas saturation was calculated by use of this conductivity model. All parameters of the model were calculated by conventional logging data. Finally, the gas content calculation model was used to evaluate a real shale gas well, and the accuracy was verified. The influence of buried depth and maturity on the gas content was also analyzed. The gas content of shale gas reservoir was calculated by using the total volume of adsorbed gas and free gas, and the result tally with the desorption gas content of core, which verifies the feasibility of this model.

Geochemical characteristics of organic-rich shales of the second member of Kongdian Formation in Cangdong Sag, Huanghua Depression

Liu Xiaoping,Liu Qingxin,Liu Jie,Dong Qingyuan,Guan Ming,Li Hongxiang

2015, Vol.27(6): 15–22 Abstract ( 485 ) PDF (672 KB) ( 1797 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.003

The organic-rich shales of the second member of Kongdian Formation （Ek2） are developed very well in Cangdong Sag, Huanghua Depression. Research on geochemical characteristics of the shales is highly significant for the shale oil resource evaluation. Based on collecting and sorting the research results of predecessors, additional core samples were taken to carry out tests and analysis of organic carbon, rock pyrolysis, chloroform bitumen “A”, kerogen maceral and vitrinite reflectance. Single well numerical simulation of burial and thermal history and geochemical evolution sections were also studied. Organic-rich shales of Ek21, Ek22 and Ek23 were all evaluated as the best source rocks. The types of organic matterare mainly of ⅠandⅡ1 , with small amount of Ⅱ2 and Ⅲ. Immature to low mature shales are mainly distributed in central uplift zone, while the organic-rich shales in slope zones are at low maturity to maturity stage. The organic-rich shales of Ek2 began to generate and expulse immature to low mature hydrocarbon in early Eocene and reached the peak in the late sedimentary period of Guantao Formation. Then with being continuously buried deeply, the source rocks could entered into low mature to mature hydrocarbon generation stage and the conversion rates of hydrocarbon generation is as high as 60%.

Provenance analysis based on rare earth element characteristics of Cretaceous sandstone （ conglomerate ） in Yaerxia area, Jiuxi Basin

Zhang Guangwei， Pan Shuxin， Wei Haoyuan， Li Wei， Zhang Liping， Long Liwen

2015, Vol.27(6): 23–29 Abstract ( 429 ) PDF (491 KB) ( 451 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.004

The Cretaceous sandstone （conglomerate） is good reservoir in Yaerxia area, Jiuxi Basin. The research on the provenance of the sandstone （conglomerate） is seldom, which restricts the sandstone （conglomerate） reservoir exploration in this area. The Rare earth element （REE） of the Cretaceous sandstone （conglomerate） in Yaerxia is analyzed, and the provenance and geochemical behavior were discussed. The results show that the content of the REE of the sandstone （conglomerate） is low, and there are no obvious differences between the Cretaceous sandstone （conglomerate） samples. The light rare earth element content obviously enriches compared with the heavy rare earth element content, with negative Eu anomalies shown in the chondrite aerolite standard pattern. The provenances supply of the sandstone may be derived from the upper crust. The Ce/Ce*and Ceanomindexes indicate that the palaeoenvironment of the Cretaceous in Jiuxi Basin was a reduction environment, and the environment is profitable for the oil and gas formation. There is no difference between the characteristics of Cretaceous sandstone （conglomerate） come from Liubei and Yaerxia.

Structure-sequence stratigraphic characteristics of the third member of Shahejie Formation in Gaoliu area, Nanpu Sag

Kang Haitao 1,2,Wang Hongyu 1,Fan Tailiang 1,Zhao Jiaqiang 1,Wang Kaijie 1,Yang Chao

2015, Vol.27(6): 30–37 Abstract ( 440 ) PDF (1188 KB) ( 417 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.005

The structure-sequence stratigraphy characteristics are necessary for subsequent study of lithologic reservoirs. Based on the 3D seismic and logging data, the regional tectonic evolution, fault development and tectonic sequence stratigraphy characteristics of the third member of Shahejia Formation （Es3） were studied, and the tectonic effect on sequence stratigraphic configuration was analyzed. The result shows that tectonic uplift and fault tilting activities occurred during the rifting process of the Es3 depositional period, which formed three “rifting and subsidence-rapid deposition-uplift and erosion” tectonic-stratigraphic cycles and corresponding three sub-structural units. The tectonic activities controlled the sedimentary sequence features of each sub-structural unit. The lateral differences of Xinanzhuang-Baigezhuang fault activities led to “see-saw” sedimentary filling characteristics of Es3. Tectonic geomorphology influenced the sedimentary system types, vertical superimposed styles and horizontal distribution characteristics.

Reservoir characteristics and development model of dense limestone ： A case study from Da ’ anzhai member in central Sichuan Basin

Ni Chao,Yang Jiajing,Chen Wei,Lin Jianping,Hou Gangfu,Wang Yong

2015, Vol.27(6): 38–47 Abstract ( 726 ) PDF (1123 KB) ( 664 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.006

The tight limestone of Da’anzhai member in the central Sichuan Basin belongs to typical “tight oil” reservoir. The reservoir lithology was reclassified to crystallized shelly limestone, argillaceous shelly limestone, micrite shelly limestone and crystalline limestone. The characteristics of four types of reservoir space were studied, including dissolved pores-vugs, secondary micropores, fractures and nanopores, and a reservoir space model for tight limestone was established, which seems like a“nets-system”. Through the analysis of the effects of sedimentary microfacies, dissolution and tectonism on the reservoir, it was pointed out that the matrix pores mainly developed in low energy shell beach, and dissolved pores-vugs mainly developed in high energy shell beach. The reservoir development model is a kind of combination by multiple reservoir space types, which distributed largely and continuously. The “sweet spot” of tight limestone is the pores-vugs-fractures reservoir developed on the area where are full of matrix pores and dissolved pores-vugs.

Cemented sealing in Kexia fault zone in northwestern margin of Junggar Basin

Cui Dian

2015, Vol.27(6): 48–54 Abstract ( 525 ) PDF (578 KB) ( 385 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.007

Kexia fault zone is a sublevel structural unit in northwestern margin of Junggar Basin. In the region from south to north, there are 5 major primary faults including Karamay fault, Nanbaijiantan fault, Baikouquan fault, Baiwu fault and Xiahongbei fault and many associated subsidiary faults. Based on the selected wells drilled cross fracture, combined with petrographic thin section and SEM analysis on the core sampling, it is found that the cement in the 5 primary faults are obviously different. From south to north, there are chlorite and laumontite, calcite, calcite and clay minerals, calcite and ferrocalcite, ankerite and siderite respectively in the 5 primary faults. It shows that from south to north diagenesis stage in Kexia fault zone tend to be late, which shows that Kexia fault zone experienced a process of cementation-denudationcementation. Combined with the analysis of fault activity and homogenization temperature test of fluid inclusions, it is considered that this is the result of differences of geofluid activity influenced by gradual advance of the fault activities.Cemented sealing of different faults and differences of geofluid activity can further affect the oil and gas distribution.

Detailed architecture analysis of mouth bar in delta front based on sedimentary process: A case study of L₁¹ layer in Laojunmiao Oilfield

Qin Guosheng 1,2,Wu Shenghe 2,Zheng Lianyong 3,Yu Chen

2015, Vol.27(6): 55–63 Abstract ( 534 ) PDF (966 KB) ( 487 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.008

Based on abundant well drilling data and geological research results in Laojunmiao Oilfield, detailed architecture analysis was carried out in the L11 layer where mouth bars are well developed. In the view of sedimentary process, the hierarchical system of mouth bar was discussed, taking the single mouth bar controlled by terminal underwater distributary channel as the third order architecture unit, the complex single mouth bar controlled by trunk underwater distributary channels as the fourth order architecture unit, and the multiple mouth bar controlled by several trunk underwater distributary channels as the fifth order architecture unit. The signs of single mouth bar were clarified, and 14 single bars were identified in the study area. According to the principle of sedimentation that bar formed in different time has different bar bottom elevation, sedimentary sequence can be constructed in the transverse section, meanwhile, the time sequence can be constructed in the longitudinal section. Integrated with 3D comprehensive analysis, the evolution time of different bars was determined. Under the guidance of the principles of sedimentology, the sedimentary process in the delta front bar was constructed. The size of single bar and the connect relationship between different bars were well coupled with the sedimentary process.

Hydrocarbon accumulation and enrichment rule of Ordovician in Yingmai - 2 area, northern uplift of Tarim Basin

Chen Siming,Hou Mingcai,Fang Qifei,Fan Shan,Yao Qingzhou,Zhou Junfeng

2015, Vol.27(6): 64–71 Abstract ( 588 ) PDF (740 KB) ( 355 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.009

In order to confirm the oil and gas accumulation rules of Ordovician carbonate reservoir in Yingmai-2 area, through the analysis of petrography and temperature features of fluid inclusion, the time-space relation for reservoirforming conditions was studied from the aspects of accumulation stages, structure, fault and reservoir. The result shows that the Ordovician reservoir in Yingmai-2 area experienced three hydrocarbon inclusions stages, including the late Caledonian-early Hercynian, the late Hercynian and the Himalayan stage. These three stages represent the oil and gas charging of three different periods and intensities, and the main stage is the intermediate oil and gas charging in late Hercynian. Under the background of structure, the oil and gas accumulation of Yingmai-2 area were controlled by space-time matching of fracture and reservoir during the main reservoir-forming period. Reservoir development and oil and gas enrichment were dominated by superimposition of fractures in three different stages. NNW and NW strike-slip fault and NE thrust-strike-slip fault played an important role in hydrocarbon migration and adjustment. The faults of three different periods met to form the fault interference zone, which can control the development and enrichment of oil and gas reservoir. On this basis, the replacing area of oil and gas enrichment of Yingmai-2 area was predicted.

Seismic sedimentology for thin sand body identification: A case study from TZ12 well block

Chang Shaoying,Zhang Xianlong,Liu Yongfu,Liu Weibo,Yu Yizhi,Shi Hongling

2015, Vol.27(6): 72–77 Abstract ( 1284 ) PDF (632 KB) ( 418 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.010

Prediction of thin sand bodies is an important issue in the fine evaluation of reservoir. Seismic sedimentology is an important research method of predicting horizontal distribution of thin sand bodies at present. But in the course of the study, there are problems that seismic data quality is poor and thin sand body description is difficult. Guided by the theory of seismic sedimentology, combined with the concept that seismic phase axis tilt angle and internal structure are controlled by frequency and 3D seismic lateral resolution is higher than vertical resolution, on the basis of classical research method of seismic sedimentology, this paper increased two technologies: frequency-broadening processing and prediction of reservoir parameters by multi-seismic attributes. Theses technologies can be used to effectively identify the lateral distribution of thin sand body and predict the thin sand body thickness and sandy ground ratio. Finally, a set of method for identifying thin layer by seismic sedimentology suitable for TZ12 well block was summarized.

Diagenesis of sandstone reservoirs of Qigu Formation in Fudong slope area, eastern Junggar Basin

Jiang Yanxia,Wen Huaguo,Zhang Haang,Liu Yapeng,Li Yun,Jin Jun

2015, Vol.27(6): 78–86 Abstract ( 518 ) PDF (1106 KB) ( 415 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.011

Jurassic lithologic reservoir is the main exploration layer in Fudong slope area of eastern Junggar Basin, so it is significant to study reservoir diagenesis for oil and gas exploration and development. Based on the analysis of thin sections, scanning electronic microscope, X-diffraction, cathodoluminescence, vitrinite reflectance and physical properties, the diagenesis and its influence on reservoir quality of Qigu Formation in Fudong slope area were detailly studied. The result shows that the sandstone reservoirs are mainly lithic sandstone, followed by feldspar lithic sandstone, which have low compositional maturity and high textural maturity. The main types of diagenetic include compaction, cementation and dissolution, and the diagenetic phase reached the middle diagenetic stage A. Among them, constructive diagenesis includes parts of chlorite envelope and illite envelope cementation and dissolution, while destructive diagenesis mainly includes compaction, multi-phase intense calcite cementation, tuffaceous cementation, siliceous cementation and analcime cementation. This study could provide reference for the reservoir prediction of lithologicstratigraphic reservoirs.

Lithofacies paleogeography of Ordovician in western Ordos Basin

Wu Xingning,Sun Liuyi,Yu Zhou,Ren Junfeng,Ding Zhenchun,Huang Zhengliang

2015, Vol.27(6): 87–96 Abstract ( 568 ) PDF (925 KB) ( 482 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.012

Based on the analysis of outcrop, drill cores, thin section and logging data, six types of sedimentary facies and ten kinds of microfacies of Ordovician were identified in western Ordos Basin. Affected by the continuous expansion of Helan aulacogen, the sedimentary models of Ordovician in northern Ordos Basin are significantly different in different periods. From the Early Ordovician to the Middle Ordovician, the sedimentary model transformed from gentle slope platform gradually to platform-slope-basin. The ramp facies of Zhuozishan Formation and platform edge facies of kelimoli Formation are mainly of limestone, bioclastic limestone and oolitic limestone, which provides an important material basis for the development of high quality reservoirs. Wulalike Formation and Lashizhong Formation developed deepwater basin facies mudstone and lime mudstone, and they are favorable facies belt for the development of hydrocarbon source rocks.

Wavelet deconvolution with spatial consistency based on CRP gathers

Ming Jun,Liu Lihui,Ding Yan,Li Cong

2015, Vol.27(6): 97–103 Abstract ( 431 ) PDF (874 KB) ( 496 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.013

When poststack wavelet extraction method of cepstrum domain is used for prestack wave extraction of CRP gathers and prestack raising resolution processing, the far and near bandwidth of the gather is not consistent, which influences the spatial consistency of wavelet and the effect of the resolution of prestack wavelet deconvolution. Therefore, this paper improved the wavelet extraction technology by using multi-cepstrum average, made the extraction wavelets have spatial consistency, and combined this improved wavelet extraction technology of cepstrum domain with spectral balance technology, to form a wavelet extraction technology which can keep the bandwidth consistent between the traces. This technology added artificial definition of the output of wavelet deconvolution, which makes it can adapt to prestack extraction frequency processing of the data with low signal to noise ratio.

Recognition and attenuation of multiples in land seismic data

Zhang Yufei,Yuan Hao

2015, Vol.27(6): 104–110 Abstract ( 431 ) PDF (1080 KB) ( 429 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.014

Multiples in land seismic data and multiples in marine seismic survey could interfere with primary reflections and resulted in low signal to noise ratio of seismic data. However, multiples in land seismic data, unlike multiples in marine seismic data, only contaminate partial continuous common midpoint （CMP） gathers rather than the whole data sets. According to the property of multiples in the land seismic data, seismic reflection characteristics of multiples in velocity spectra, constant-velocity scan sections and normal movement correction gathers were analyzed. The CMP ranges were determined in the seismic data by multiple recognition methods, and the parabolic Radon transform was used to suppress multiples in the NMO gathers with multiples. The results of synthetic and field seismic data processing show that parabolic Radon transform method could suppress the multiples of land seismic data, and does not damage the primary reflections during multiple processing, achieving the effect of fidelity denoising.

Application of ant tracking technology to fracture prediction:A case study from Xiagou Formation in Qingxi Oilfield

Zhou Wen， Yin Taiju， Zhang Yachun， Li Weiqiang， Wang Dongdong

2015, Vol.27(6): 111–118 Abstract ( 482 ) PDF (750 KB) ( 483 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.015

The main reservoirs of the Low Cretaceous Xiagou Formation are characterized by muddy dolomite with low porosity and low permeability and conglomerate in Qingxi Oilfield, where fractures act as important migration and accumulation space and have controlling effect on oil enrichment. Ant tracking technology and imaging logging data were applied to analyze the characteristics of the fractures in Qingxi Oilfield. The fractures distribution of Xiagou Formation was predicted and the fracture model of Qingxi Oilfield was established. The results show that the study area mainly developed two sets of fractures including NE-SW trend and NW-SE trend, the fractures developed with high degree are mainly located in the northwest, northeast and southeast of Qingxi Oilfield, and high yielding wells are mostly located in these areas. Consequently, the areas with high degree development of fracture are favorable for oil and gas exploration and development at the late stage.

Reservoir characteristics of oil sands and logging evaluation methods:A case study from Ganchaigou area, Qaidam Basin

She Gang,Ma Lijuan,Xu Yongfa,Ye Gaopeng,Mi Xiaoyin,Li Chengyuan

2015, Vol.27(6): 119–124 Abstract ( 484 ) PDF (475 KB) ( 351 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.016

Qaidam Basin is rich in oil sand resources, but at present there is no systemic method for logging evaluation. Based on the existing geological and logging data, the mineral composition, physical properties and oiliness of the oil sand reservoirs in Ganchaigou area were analyzed. It is considered that porosity and oil content are the main factors of the oiliness of oil sands. By logging data, the calculation models of porosity and oil content were established with higher accuracy. By means of constructing the concept of synthetic oil-bearing index, combined with porosity and oil content, the interpretation charts and classification criterion of oil sands were established, and good effect was achieved in the actual production.

Theory of unsteady reservoir and its application in A oilfield of Iran

Chen Jie,Du Yang,Peng Pai,Huang Hexiong,Tong Mingsheng,Xiong Shu

2015, Vol.27(6): 125–131 Abstract ( 427 ) PDF (748 KB) ( 418 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.017

The oil-water contract （OWC） of Sarvak reservoir of A oilfield in Iran is characterized by a large-amplitude one tilting from north to south. The hydrodynamic force is not the cause and the reservoir heterogeneity is not the main reason for the tilted OWC of the Sarvak reservoir. The main reason for the large-amplitude tilted OWC is the structure adjustment. Based on the analysis of sedimentary and tectonic evolution, formation flattening technique is utilized to recover the paleo-structure of different geologic stages. Combined with accumulation factor analysis, it is considered that the adjustment of traps is caused by Zagros orogeny and the structure adjustment rate is faster than the hydrocarbon adjustment rate. Now, the Sarvak reservoir is still in the new condition of migration, accumulation and adjustment, which is an unsteady reservoir. A paleo-trap which decreased from north to south formed in the Sarvak Formation in A oilfield after the late Paleocene. The Zagros orogeny during the Neogene caused the adjustment of the trap, and the former low point in the south uplifted significantly and gave birth to a new secondary trap. So, today the structure in the south of Sarvak Formation is higher than that in the north. The balance in the paleo-trap was broken, and hydrocarbon migrated to the secondary trap in the south. The large-amplitude tilted oil-water contract showed that the paleoreservoir was still adjusting and unstable. The favorable development zone is the high zone of paleostructure which is in the western Sarvak reservoir, followed by the belt of transition between paleostructure and current structure.

Geosteering technology of horizontal well and its application in Sulige Gas Field

Sun Weifeng，Zhang Ji,Ma Zhixin,Hao Qian,Shi Linhui,Zhang Zhigang

2015, Vol.27(6): 132–137 Abstract ( 496 ) PDF (582 KB) ( 379 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.018

Sulige Gas Field is a typical tight gas reservoir characterized by low permeability, low pressure, low abundance and strong heterogeneity. Horizontal well development is significant for well production increase. However, horizontal well drilling Geosteering difficulty is the bottleneck restricting the development of efficient technologies. There are problems such as mudstone interlayers, difficulties for judging structure and bottom lithology during the process of drilling geosteering. On the basis of deployment and design of horizontal well technology, by analyzing the specific circumstances of the horizontal section drilling mud, combined with the analysis of vertical stacking sand relations and internal reservoir, this paper summarized a set of adjustment measures of horizontal section guiding suitable for gas reservoirs of He 8 member, and illustrated by taking the actual drilling from AH well as an example. The development of horizontal wells for many years proved that by using geosteering technology for horizontal well development, the average sandstone drilled rate can reach 85.7%, the average effective reservoir drilled rate is 62.5%, and horizontal well production is 3 to 5 times than that of vertical well.

Production decline trend of shale gas

Zhang Diqiu,Li Zhiping,Su Hao

2015, Vol.27(6): 138–144 Abstract ( 613 ) PDF (439 KB) ( 1079 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2015.06.019

Shale gas reservoir has low permeability, in which fluid hardly flow and wells have smaller production capacity. The production decline trend of shale gas reservoir is largely different from conventional gas reservoir. The study on shale gas production decline trend is a reference to predict future production changes, development indices and indicators, subsequent adjustment of development measures. Based on Arps decline equation and generalized Weng’s model, a new model, compound decline model was proposed. Because the compound decline model has more general applicability rather than Arps decline equation, it was applied to shale gas production decline trend analysis in this paper for the first time. Then the changing parameters and influencing factors of compound decline model and Arps decline equation used on shale gas production were computed and analyzed. Comparing the compound decline model with the Arps decline equation in case of practical application in Haynesville shale and Barnett shale, it was tested and verified that there are great differences between the production decline trends of two categories of shale gas field.