Lithologic Reservoirs

Based on the analysis of lithostratigraphic gas reservoirs exploration course in China from initially discovery to development, lithostratigraphic gas reservoirs are considered to take a significant contribution to the reserves increase. According to the study on the distribution characteristics, the lithostratigraphic gas reservoirs in China mainly distribute in large palaeohigh and slope in craton basin and special lithosome in fault depression, which will be the main fields for searching for large lithostratigraphic gas reservoirs.

Control of base level cycles on channel sand geometry:A case study on ZaoⅡ-Ⅲ reservoirs, Zaoyuan Oilfield

ZHANG Changmin, YIN Taiju, LI Shaohua, XIONG Fujun

2007, Vol.19(4): 9–12 Abstract ( 519 ) PDF (577 KB) ( 640 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.002

Reservoirs of ZaoⅡ and Zao Ⅲ of the first member of Kongdian Formation in Zaoyuan Oilfield are dominated by channel sands developed on alluvial fans. Three long-term base level cycles and 11 middle-term base level cycles are recognized in ZaoⅡ and ZaoⅢ reservoirs, and each middle-term cycle is composed of one to five short-term base level cycles. Short-term cycles can be divided into high and low accommodation space cycles which represent two kinds of channel sand bodies with ifferent characteristics. Middle-term cycles can be classified into symmetry and asymmetry types. Sediments at high accommodation stage of long-term cycle are mainly mud, with single channel inserted in. With the rise of the long-term base level, the ratio of width to thickness of sand bodies increases and sand content decreases.

“Multi-factor controlling, four-factor entrapping and key-factor enrichment” of stratigraphic-lithologic reservoirs and exploration practice in Erlian Basin ( Ⅲ)———“Key-factor enrichment” mechanism

WANG Quan, LIU Zhen, ZHAO Xianzheng, JIN Fengming, LIANG Hongbin,YANG Dexiang

2007, Vol.19(4): 13–19 Abstract ( 475 ) PDF (908 KB) ( 382 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.003

Based on the analysis of the enrichment factors for stratigraphic-lithologic reservoirs found in Erlian Basin, the enrichment of the stratigraphic-lithologic reservoirs is considered to be controlled by three main factors, including abundant oil sources, high quality sand body traps and main confluent passageway. Abundant oil sources are the background for the enrichment; high quality sand body traps which spread broadly are the key point for the enrichment; and the main confluent passageway is the best way for enrichment of the stratigraphiclithologic reservoirs.

Paleosalinity analysis and trace element geochemistry of Chang 6 member in Gengwan-Shijiawan area, Ordos Basin

HAN Yonglin, WANG Haihong, CHEN Zhihua, WANG Fang, LIANG Xiaowei,WANG Chengyu, NIU Xiaobing

2007, Vol.19(4): 20–26 Abstract ( 555 ) PDF (551 KB) ( 707 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.004

The trace element geochemistry methods such as B, Sr, Rb and K+Na mass fraction, Sr/ Ba ratio, Rb/K ratio combining with clay mineral X -ray diffraction analysis are applied to analyze the paleosalinity of Chang 6 in Gengwan-Shijiawan area. The result shows that in the period of Chang 6 stage, it is fresh -mildly brackish environment, partly brackish environment with the paleosalinity from 0.014‰ to 6.47‰ , average of 2.56‰, and the water is saltier gradually from the period of Chang 63 to Chang 61. The paleosalinity isolines are mapped after recovering the paleosalinity quantitatively, in which three paleosalinity zones are divided, including fresh water zone, mildly brackish water zone and brackish water zone. And 0.5‰ isoline is determined to be the position of lake shoreline which is the boundary of fresh water river and mildly brackish lake. The mildly brackish water and close environment are favorable for the development of the high quality source rocks, and could promote the forming of the early chlorite rim cementation to retard the compaction and dissolution which is helpful for preserving primary intergranular pores. So it provides important evidence for the favorable target prediction of lithostratigraphic reservoirs.

Geological techniques for Triassic lithologic reservoirs in Ordos Basin

MAO Minlu, YANG Yajuan, ZHANG Yan

2007, Vol.19(4): 27–33 Abstract ( 493 ) PDF (443 KB) ( 489 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.005

Lithologic reservoirs of Triassic Yanchang Formation of Mesozoic in Ordos Basin are characterized by low and extra- low permeability, which is famous for fracturing treatment. Geological techniques applied in deposition and reservoir genetic factors analysis are studied from the aspect of practicability. Several simple and practical geological methods are selected and developed, which include the analysis methods for structural setting and basin tectonic type in well developed deposition, source origin, depositional environment dominated by rock texture, sequence stratigraphy of continental facies lake basin, sequence and plays. These geological techniques will take a significant part in studying accumulation rules for lithologic reservoirs. Good results have been achieved in the practical application in Ordos Basin.

Reservoir characteristics of N₁—N₂¹ in Shaxi zone of Gasikule Oilfield

HE Hui, MOU Zhonghai, ZHU Yujie, CHI Hongyan, LIU Dongxi

2007, Vol.19(4): 34–39 Abstract ( 554 ) PDF (384 KB) ( 446 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.006

The data of thin section, cast slice, SEM, X-ray diffraction, mercury injection combining with geological information and physical properties analysis are applied to analyze the characteristics of N1—N21 and the difference between the upper wall and lower wall of fault Ⅱ in Shaxi zone. The result shows that the reservoir in the study area is clastic reservoir which experienced destructive diagenesis of compaction and cementation and constructive diagenesis of dissolution and tectonism. The diagenetic stage is in the period from early diagenesis subage B to late diagenesis subage A1. The pore structure types are intergranular pore, intragranular pore, and fracture etc. The reservoir of N1—N21 is middle pore and low permeability reservoir with poor property. Distributary channel sand bodies are the foremost reservoirs in the study area. The compositional maturity of the lower wall is much better than that of the upper wall of fault Ⅱ, however the cement content is on the contrary. The sandstone in upper wall is mainly the feldspathic litharenite, and in the lower wall it is mainly the arkose. The pore in upper wall is mainly intergranular pore, however, fracture developed well in lower wall. The reservoir is medium porosity and medium permeability in upper wall but low porosity and low permeability in lower wall.

Micro-fractures in extra-low permeability reservoir of Yanchang Formation in Ordos Basin

NAN Junxiang, WANG Surong, YAO Weihua, LU Yan

2007, Vol.19(4): 40–44 Abstract ( 559 ) PDF (647 KB) ( 747 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.007

Micro- fracture is one of the main flow passages for low permeability reservoir. The reservoir of Yanchang Formation in Longdong area is extra- low permeability reservoir. By using the frequency analysis methods such as polarizing microscope and SEM, the occurrence, features, surface density, planar distribution rules and the contribution to permeability of the micro- fractures are analyzed. It points out that the microfractures are widely developed in this area and controlled by factors of sedimentation, diagenesis, tectonic lateral compression, mineral component, structural tectonics, hidden fracture of underlying strata and so on. The surface density of the micro- fracture is closely related to the permeability. Micro- fracture is the key factor which should be considered in oilfield development and deployment.

Influencing factors and characteristics of Chang 6 reservoir in Wuqi area, Ordos Basin

WEI Qinlian, ZHENG Rongcai, XIAO Ling,WANG Chengyu, NIU Xiaobing

2007, Vol.19(4): 45–50 Abstract ( 545 ) PDF (631 KB) ( 821 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.008

Based on the analysis of cast slice and petrophysics, the petrology characteristics, porosity and permeability, pore structure and pore types of Chang 6 reservoir in Wuqi area are studied, and its influencing factors are analyzed. The result shows that Chang 6 reservoir is characterized by low mineral maturity and high structure maturity, medium porosity and low permeability with intergranular pore and solution pore developed well. Medium pore and small pore are the main reservoir space. Fine throat and middle throat are the basic seepage passage. The reservoir property is closely related to both sedimentary microfacies and diagenesis. It is affected by sedimentary facies belt on plane, and made poor by compaction and cementation in vertical direction, however, improved by secondary pores caused by dissolution.

Classification method for extra-low permeability reservoirs

YANG Qiulian, LI Aiqin, SUN Yanni, CUI Panfeng

2007, Vol.19(4): 51–56 Abstract ( 580 ) PDF (434 KB) ( 884 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.009

Aimed at the shortage of classification evaluation for extra- low permeability reservoirs, several new techniques developed in reservoir research are introduced in recent years. Four classification evaluation parameters for extra-low permeability reservoir are proposed, including effective porosity, mainstream throat radius, movable fluid saturation and start-up pressure gradient. The reservoir classification evaluations are carried out to nine blocks. The results show that the seepage capacity and effective reservoir space could be effectively reflected. This classification method will be important to guide the oil/ gas field development.

Using multi-parameters analysis of seismic information to evaluate lithologic traps in continental basins

YANG Zhanlong,ZHANG Zhenggang,CHEN Qilin,GUO Jingyi,SHA Xuemei,LIU Wensu

2007, Vol.19(4): 57–63 Abstract ( 493 ) PDF (335 KB) ( 580 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.010

The lithologic traps in continental basins are characterized by complex boundary condition, irregular shapes, subtle occurrence, complex accumulation and various migration mechanisms, and the features of itself are of small area, thin reservoir and occurring in group. According to all these characteristics, it is proposed that the selection of seismic data, calibration of horizon and reservoir, interpretation of top and bottom controlling horizons and determination of time window are the key factors for the lithologic traps identification, optimization, description and evaluation with multi-parameters analysis of high-resolution 3D seismic. The multi-parameters analysis methods include seismic facies classification, seismic inversion and reservoir prediction, seismic attributes analysis, fluid potential analysis, hydrocarbon detection and 3D visualization. Since the lithologic reservoir exploration is at the beginning stage, the related technological specifications and criterions are still need to be improved.

Sequence-based lithofacies and paleogeography of Lower Triassic Feixianguan Formation in northeastern Sichuan Basin

LI Guojun, ZHENG Rongcai, TANG Yulin, WANG Yang, TANG Kai

2007, Vol.19(4): 64–70 Abstract ( 507 ) PDF (688 KB) ( 724 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.011

Based on the study of sequence stratigraphy, Feixianguan Formation is divided into two third-order sequences ( SQ1, SQ2) and eight system tracts, of which the lithofacies and paleogeography are analyzed. During the first deposition of the third-order sequence cycles ( SQ1) , influenced by the regional tectonic uplifting in Changxing stage of Late Permian in northeastern Sichuan, the seawater once deep and wide became shallow, and the depositional evolution changed from basin facies to open-platform facies, of which oolite beach developed well. During the second deposition of the third-order sequence cycles ( SQ2) , due to arid and hotter climate, fallen sea level, limited water cycle and exposed carbonate platform, the depositional evolution became to restricted platform and evaporated platform facies, and the oolite beach in northeastern Sichuan decreased. Finally, the sedimentary geomorphology was nearly full filled.

Seismic sequence of Triassic Yanchang Formation in Ordos Basin

ZHANG Jie, ZHAO Yuhua

2007, Vol.19(4): 71–74 Abstract ( 476 ) PDF (535 KB) ( 575 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.012

According to Cross theory on high resolution sequence stratigraphy, Triassic Yanchang Formation is divided into one second-order sequence and five third-order sequences. The top boundary of the secondorder sequence is the unconformity between Jurassic and Triassic, the bottom boundary is the bottom of Yanchang Formation, and the maximum flooding surface is Zhangjiatan shale which distributes broadly in the basin. The third-order sequences can be identified by the surface of interrupted deposition, flooding surface, scour surface, sedimentary transformation surface and lithology transformation surface. The characteristics of sequence boundary surface in seismic profile are concluded. According to these characteristics, the seismic profile is interpreted and the evolution of Yanchang Formation in vertical direction is analyzed.

Depositional system of the Neogene shallow water delta in Bohai Sea area

DAI Liming, LI Jianping, ZHOU Xinhuai, CUI Zhongguo, CHENG Jianchun

2007, Vol.19(4): 75–81 Abstract ( 513 ) PDF (769 KB) ( 738 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.013

The sedimentary facies of Neogene in Bohai Sea area used to be considered as fluvial facies over a long time. Results of exploration in recent two years indicate that shallow lake is widely developed in the Neogene in Bozhong Sag and Huanghekou Sag in Bohai Sea area, in which a kind of excellent reservoir is also found—shallow water deltaic sand bodies. It is proved that the shallow lake exists in the Neogene in Bohai Sea area by the evidence of paleontological assemblages, characteristics of mudstone, litho-electric relationship, sand percentage, sand grain size, sedimentary structure. Shallow water delta is developed in the river mouth around the shallow lake which can be identified with sedimentary sequence and types of sedimentary facies. Being different from the classical Gilbert delta, shallow water delta is with thinner mouth bar and broadly spread sheet sands, and displays that the facies sequence is discontinuous in vertical direction, and the matrix sand bodies are distributary channel sand bodies. The type of the shallow water delta is fluvial-dominated delta.

Fine stratigraphic classification and correlation of Chang 3 reservoir of Yanchang Formation in Zhenbei Oilfield

ZHU Xiaoyan, LI Aiqin, DUAN Xiaochen, TIAN Suiliang, LIU Meirong

2007, Vol.19(4): 82–86 Abstract ( 440 ) PDF (406 KB) ( 539 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.014

Based on well logs and core data, the characteristics of the rock-electric property of more than 100 wells are analyzed. The fine stratigraphic classification and correlation of Chang 3 reservoir in Zhenbei Oilfield are carried out. From top to bottom, Chang 3 can be divided into Chang 311, Chang 312, Chang 313, Chang 321, Chang 322, Chang 323, Chang 331, Chang 332 and Chang 333. Among them, Chang 322 and Chang 331 are underwater distributary channel deposits, and with sand bodies developed well, they become the dominated reservoirs in the study area. The fine classification and correlation can provide geologic basic data for the study on sedimentary microfacies, sand body distribution, reservoir heterogeneity and favorable target prediction, which takes a significant part in the oilfield development.

Maceral and petrology of Lower Tertiary source rock in Qintong Sag, Subei Basin

FANG Chaohe, WANG Yifeng, ZHENG Dewen, GE Zhixin

2007, Vol.19(4): 87–90 Abstract ( 467 ) PDF (313 KB) ( 886 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.015

The bulk-rock analysis technology of organic petrology is applied to analyze the macerals of source rocks in different formations in Qintong Sag. Based on the organic geochemistry analysis, it is concluded that the content of exinite, alginate and mineral bituminous matrix can reflect the hydrocarbon generation potential and genetic types. Mineral bituminous matrix is the main hydrocarbon generation component in source rock of Taizhou Formation, Qintong Sag.

Application of prestack inversion in Sulige area

ZHANG Mengbo, SHI Songqun, PAN Yu

2007, Vol.19(4): 91–94 Abstract ( 465 ) PDF (544 KB) ( 578 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.016

The effective reservoir in the eighth member of Shihezi Formation in Sulige area is characterized by thin thickness, rapid lateral variation. Based on logging and petrophysics analysis, the elastic parameters ( such as elastic impedance, Poisson’s ratio and so on) of the effective reservoir are obtained by prestack inversion, and fluid properties are analyzed, which can provide reference for drilling well location. Good result has been achieved in well location optimization in Sulige Gas Field.

A theoretical formula of stress sensitivity index with compressibility of rock

LI Chuanliang

2007, Vol.19(4): 95–98 Abstract ( 616 ) PDF (271 KB) ( 642 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.017

Permeability of rock will change with the stress applied on, which is called the stress sensitivity of reservoir rocks. Stress sensitivity of rock is closely related to its compressibility. The more compressible the rock is, the higher the stress sensitivity index will be. A theoretical formula is proposed between the stress sensitivity index and the compressibility of rock. According to this formula, due to the weak compressibility of rock, the stress sensitivity is extremely minus, which can be neglected in production of reservoirs.

3D reservoir geologic modeling and potential tapping in glutenite reservoir :A case study from conglomerate reservoirs in Karamay Oilfield

SONG Ziqi, YI Junfeng, PANG Zhenyu,WANG Yan, LI Weifeng

2007, Vol.19(4): 99–105 Abstract ( 443 ) PDF (518 KB) ( 689 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.018

The heterogeneity of conglomerate reservoir is studied by 3D geologic modeling. The main potential tapping and potential zone are illustrated. The 3D geologic modeling includes reservoir structure modeling, sedimentary microfaciesmodeling and reservoir parameter modeling. The structure modeling achieves the intercalibration process of fault-point data and individual layer data derived from seismic interpretation and drilling. Sedimentary microfacies modeling displays the reservoir volume, geometric shape and 3D distribution. Reservoir parameter modeling carries out the reservoir parameter model constrained by facies belt distribution range, original reservoir data and 3D geologic interpretation. The result shows that the modeling overcomes the disadvantage caused by various data with different resolution, optimizes the geologic modeling for heterogeneity conglomerate reservoir suitable for practical production, and indicates the potential zone and reservoir range controlled by favorable sedimentary facies belt.

Flow unit method for calculation of single well controlled reserves in low permeability gas field

SHI Yucheng, CHEN Mingqiang, ZHANG Shenqin, LEI Xinhui, WANG Qi

2007, Vol.19(4): 106–110 Abstract ( 517 ) PDF (523 KB) ( 617 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.019

Low permeability reservoir is characterized by poor physical properties, heavy heterogeneity, natural micro-fracture and connectivity anisotropy etc. The result will not conform to the real value if we simply calculate the single well controlled reserves by the conventional way of dividing the oil area. According to theory of flow unit dividing and the characteristics of low permeability reservoir, the flow unit method is put forward. It is to divide the flow units, and then calculate the single well controlled reserves regarding the flow unit as the calculating unit, finally, compare and analyze the results from this method, single well controlled area method and dynamic pressure drawdown method respectively. The comparison result proves the scientificity and practicability of the flow unit method.

Determination of the proved reserves area of low permeability reservoirs in Daqing Oilfield

ZHOU Yongbing, LIU Guozhi, YU Jing

2007, Vol.19(4): 111–115 Abstract ( 504 ) PDF (142 KB) ( 644 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.020

Based on the analysis of distribution characteristics of proved reserves of low abundance reservoirs in Daqing peripheral oilfield, the main principles and methods for determining oil-bearing area of proved reserves of low permeability reservoirs in northern Songliao Basin are summarized. According to the change of area after the exploitation in typical blocks, the influence of wells per square kilometer on the determination of oil-bearing area is analyzed. The quantity of drilling wells per square kilometer is considered to be controlled by the size and shape of sand and the type of reservoir in northern Songliao Basin. It should be increased to 0.5 to 1.0 per square kilometer in the evaluation stage for lithologic reservoirs.

Optimization of upward strata combination of second class oil layer in eastern south Ⅱ area of Daqing Oilfield

ZHANG Liqiu

2007, Vol.19(4): 116–120 Abstract ( 438 ) PDF (324 KB) ( 387 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.021

Polymer flooding of the first class oil layer is on the decrease in Daqing Oilfield, and the development techniques of the second class oil layer are in developing at present. The second class oil layer is characterized by decreased channel sand, increased sublayers, thinning single layer, low permeability. In order to enhance oil recovery, the strata combination is analyzed based on the study on layer selection criterion, deposition characteristics and the influencing factors. The thickness of the upward strata and the producer-injector spacing are determined, which will provide reference for the strata combination in this area.

Application of heat-resistant and salt-tolerant particle profile control and displacement agent in Wennan Oilfield

WANG Fei, XU Yuangang, WAN Lingxia, ZHANG Hebin

2007, Vol.19(4): 121–127 Abstract ( 417 ) PDF (283 KB) ( 479 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.022

Wennan Oilfield is a typical reservoir characterized by high temperature and high salinity. It is now in high water cut period, with water flooding already in the main formation. Particle profile control and displacement agents are developed to improve the oilfield development effect. The tests on heat stability, saltresistant capability and rate of expansion show that the profile control and displacement agents with a good performance of salt-tolerant and heat-resistant are suitable to the formation characteristics of Wennan Oilfield. Aimed at the main object of profile control and displacement which is to find and recover the residual oil, the principles for selecting profile control and displacement blocks are determined. Water drive front and real time monitoring technologies are adopted in the practical operation, and the relevant satisfactory results are obtained.

Cultivation of explorer ’s comprehensive quality ( Ⅰ)

ZHANG Xia

2007, Vol.19(4): 128–130 Abstract ( 350 ) PDF (170 KB) ( 362 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2007.04.023

As a kind of creative activity, exploration requires explorers to have better comprehensive quality. In order to improve the comprehensive quality, both science and culture should be paid attention to. The cultivation of science spirit, humanism spirit and scientific way of thinking is stressed here. The corresponding value evaluation standard and motivation system should be established to overcome the effects of hierarchical culture, improve philosophy quality, thinking quality and human character. Working style should be changed to save space for improving human’s quality.