Petroleum Exploration and Development

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Application of fenugreek gum fracturing fluid in deep wells of Changqing Oilfield

TANG Meirong; LU Hongjun; MA Jianjun and LIU Daozhong

, 2008, 35(3): 1577-0.

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Fenugreek gum, which has rich Polygalacto-mannitose, is a sort of natural vegetable gum. It is planted and processed in China and can be used as the viscosifier of the water-base fracture fluid after processing and modifying. The borax cross-linked fracture fluid of fenugreek gum possesses nice performance. The experimental evaluation of the fracture fluid's rheology, carrying capacity, gel-breaking, filtration, etc. shows that its performance is close to guar gum fracturing fluid and even better than the guar gum fracturing fluid in some aspects. Testing in deep wells of the Changqing oil field shows that the fenugreek gum fracturing fluid meets the demands of fracturing and transporting sand, increasing production, and reducing the cost. With large-scale production, its price will be more competitive than guar gum. With China's low permeability reservoirs' development and the increasing of hydraulic fracturing, it holds wide prospects for application.

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Formation and distribution of volcanic hydrocarbon reservoirs in sedimentary basins of China

ZOU Caineng; ZHAO Wenzhi; JIA Chengzao; ZHU Rukai; ZHANG Guangya; ZHAO Xia and YUAN Xuanjun

, 2008, 35(3): 1598-0.

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Volcanic hydrocarbon exploration in China experienced three phases, accidental discovery, local prospecting and all-round exploration. There are mainly Carboniferous-Permian, Jurassic-Cretaceous, Paleogene-Neogene volcanic rocks and lava, pyroclastics, karst reservoirs in oil- and gas-bearing basins in China. Volcanic rocks can not generate organic hydrocarbons, and the combination of volcanic rocks, source rocks and seals is the key controlling factor of the primary lava plays. The near-source play is most favorable for hydrocarbon accumulation. Distribution of oil and gas is controlled predominantly by the hydrocarbon-generating center. The distal play requires communication with faults or unconformities. Near-source plays are in the faulted basins in eastern China. Structural-lithologic hydrocarbon reservoirs are formed in the higher place of faults and lithologic hydrocarbon reservoirs are formed in the slope. Two types of plays are developed in central and western China. The near-source play is most favorable for the formation of large stratigraphic hydrocarbon reservoirs.

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Division and evaluation of oil-gas prolific zones for litho-stratigraphic reservoirs in the Nanpu Sag

XU Anna; DONG Yuexia; ZOU Caineng; WANG Zecheng; ZHENG Hongju; WANG Xudong and CUI Ying

, 2008, 35(3): 1599-0.

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The Nanpu Sag is a typical lacustrine downfaulted hydrocarbon-rich depression. Some litho-stratigraphic reservoirs have been discovered there in recent years. Based on "Sag-wide Oil-bearing Theory" and petroleum system, the concept of "play" is used as a unit for the division and evaluation of oil-gas prolific zones in this paper. The overlaying technique of "four maps", which are the fault structure map, the sedimentary facies map, the major effective source-rock distribution map and the current exploratory situation map, is applied to the comprehensive evaluation of oil-gas prolific zones. The Nanpu Sag is divided into three first-order plays in vertical, namely above-source play, in-source play and below-source play, and each of them can be subdivided into second-order plays. The above-source play is divided into eight oil-gas prolific zones and four favorable areas are evaluated. The in-source play is divided into six oil-gas prolific zones and four favorable areas are evaluated. The below-source play is divided into two parts with ten oil-gas prolific zones and five favorable areas are evaluated.

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Organic biofacies of Jurassic source rocks in northern Qaidam Basin， NW China

LIU Yuntian; HU Kai; CAO Jian; YANG Shaoyong; BIAN Lizeng; WANG Liqun and CHEN Yan

, 2008, 35(3): 1600-0.

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Organic petrological microscopic observation indicates that algae, cutinites and sporophytes are the main organic macerals of Jurassic mudstone source rocks in the northern Qaidam Basin. According to the occurrence and abundance of these three types of macerals in rocks as well as their relative contents, the hydrocarbon-generating biofacies are divided into four types: A (algae-bed), B (dense transport-deposit algae), C (sparse transport-deposit algae) and D (algae-bits). From type-A to type-D rocks, the organic matter abundance gradually decreases, and the quality gets poor. The type-A source rock has the best generative potential, with TOC higher than 4.0% and organic matter types of Ⅱ1-Ⅱ2. It occurs only in parts (with ca. several to tens of meters) of the Lower Jurassic and the Seventh Member of Middle Jurassic strata, implying the heterogeneity of source rocks. Lagoon environments of lake-deltaic sedimentary systems are good for its deposition.

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Exploration potential of Chang 9 member, Yanchang Formation, Ordos Basin

ZHOU Jingao; YAO Genshun; DENG Hongying; XIN Yongguang; HU Heng; ZHENG Xingping and GONG Qingshun

, 2008, 35(3): 1601-0.

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New discovery has been achieved in the exploration of the Chang 9 member, Yanchang Formation. This article discusses the exploration potential of the Chang 9 member from hydrocarbon source rock condition, reservoir condition and the pattern of hydrocarbon generation and storage. The Chang 9 member develops high quality hydrocarbon source rock (the mean TOC is 4.36% and Ro is 0.66%-1.01%), has superior hydrocarbon-offering capacity, and the total resources surpass 402 million tons of oil. Delta front subaquatic distribution channel sandstone and river mouth bar sandstone can be connected as a complex laterally and the main reservoir space is remnant primary pores. The reservoir capability is good. The member develops 3 types of plays: self-generation and self-storage, below-generation and above-storage, above-generation and below-storage. The exploration potential of the self-generation and self-storage is best with dark mudstone or oil shale as the source rock and sandstone as the reservoir.

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Distribution and accumulation of the oil and gas in southern Huanghua Depression

QU Fang; CHEN Qinghua; LIAN Chengbo; ZHANG Juntao and CAI Fulong

, 2008, 35(3): 1602-0.

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On the basis of oil and gas distribution in southern Huanghua Depression, the hydrocarbon accumulation conditions and developing characteristics of the main faults in different stages are researched. The mechanism of source faults accumulating hydrocarbon is analyzed. The seismic pumping mechanism of long-term developing source faults is the main driving force of hydrocarbon accumulation. The sources of seismic pumping control the horizontal distribution of hydrocarbons, while the sources of seismic pumping and the secondary seismic pumping sources produced by the main tensional layer control the lengthways accumulation of oil and gas. The reservoir sands or oil traps near the seismic pumping region might be the most efficient fields for hydrocarbon accumulation. Hydrocarbons sourced from the second member of the Kongdian Formation are mainly distributed at the southwestern tail of the Kongxi fault and the fault rapidly decreased displacement or the abruptly changed strike of the Kongxi, Fenghuadian and Kongdong faults. The main tensional layer of the upper part of the first member,Kongdian Formation accumulates large quantities of oil and gas.

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Petroleum migration in the Gasikule Oilfield, Qaidam Basin, NW China

ZHANG Chunlin; GAO Xianzhi; LI Yanfei and MA Dade

, 2008, 35(3): 1603-0.

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Gasikule Oilfield is an area rich in oil and gas in the Qaidam Basin and contains the E31 and N1-N21 oil reservoirs. Through conventional column chromatographic extraction of 48 oil samples, this paper investigates the oil migration and charge direction using the nitrogen compounds, the sandbody distribution in E31 and N1-N21, and the E31 reservoir dissection. Oil in the Ⅰ＋Ⅱ and Ⅲ＋Ⅳ oil layers of the E31 reservoir migrates from middle-north of the anticline to its south and north, and its oil source areas are the Mangya Sag and the Gasi rift-subsidence. The injection spots of the Ⅰ＋Ⅱ oil layer are the two sides of Well 9-7 in the middle of the anticline, and the injection spots of the Ⅲ＋Ⅳ oil layer are Wells 8-34 and 9-38. The N1-N21 reservoir oil is mainly from the Mangya Sag and migrates to reservoirs upwards along faults. Faults and sandbodies are the main transport channel in the field and most reservoirs are anticlinal.

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Genesis and distribution of secondary porosity in the deep horizon of Gaoliu area, Nanpu Sag

ZHANG Wencai; LI He; LI Huijun; MENG Yuanlin and YANG Fengbo

, 2008, 35(3): 1604-0.

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Strong dissolution generates a secondary porosity interval at 3 250-3 800 m in deep sandstones of the Shahejie Formation in the Gaoliu area. The secondary pores include intraparticle pores, interparticle pores, moldic pores, and dissolved cement pores and fractures. The underground water of the Gaoliu area is fed with fresh water in the northern Yanshan folded mountains. The fresh water moves along the deep and big faults such as Baigezhuang, Xi’nanzhuang etc. under the gravity force, and then moves along with uncomformities. The secondary porosities of deep horizon sandstones are formed by the leaching of ground water along these faults and uncomformities during the shallow burial process, and preserved by the abnormal high pressure during the deep burial process. Faults and uncomformities, served as the leaching path of ground water, alone with the abnormal high pressure, control the secondary porosities distribution. Good reservoirs are possibly at places near the Gaobei fault, the footwall of the Shuohe fault, the Tanghai area, and the Shichang subsag near the footwall of the Baigezhuang faults.

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Prediction of effective fractures in a limestone buried hill, South China Sea

CHEN Guangpo; WANG Tianqi; LIU Yingru; SHI Lanting and MA Long

, 2008, 35(3): 1605-0.

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Because of the strong tectonic movement during the formation of a limestone buried hill in the A sag, lots of fractures occured. The early formed structural fractures have undergone denudation, demorphism, leaching, dissolution from atmosphere precipitation and surface runoff, which make some of the initial structural fractures enlarged and some half-filled or full filled with calcite. The fractures formed in the later tectonic movement are generally not filled and become the main channel connecting dissolution pores with cavities. This paper calculates the strain magnitude of buried hill formations resulting from every tectonic movement using strain analysis methods such as the inversion and forward modeling of structural evolution history of formations, predicts the 3D fracture network formed in every tectonic movement from the geological genesis standpoint, and therefore, distinguishes the early filled fractures formed in the period of the buried hill formation from the unfilled fractures formed later, achieving the goal of predicting fracture reservoirs in the limestone buried hill.

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Advances on special structure drilling development techniques in Shengli Oilfield

ZHOU Yingjie

, 2008, 35(3): 1606-0.

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Shengli Oilfield has developed the reservoir engineering design and drilling-completion-production techniques of special structure drilling for reservoirs with bottom water, fault block, heavy oil, unconformity etc., and drilled different types of wells including horizontal well, sidetracked well, extended reach well, multi-lateral horizontal well and so on. There are 586 different horizontal wells in 181 development units of different types, and 742 sidetracked wells in 284 development units. The annual oil production is 1.19 and 0.79 million tons, respectively, and the cumulative oil production 8.25 and 4.09 million tons. The special structure drilling has become one of the dominant techniques for the stable production and production growth of the field. New advancements have been achieved in the reservoir description, reservoir engineering design, well drilling technology, well completion technology and producing technology for thin-layer reservoirs, high-watercut thick-layer positive rhythm reservoirs, buried hill heavy oil reservoirs, extra-heavy oil reservoirs, and complicated fault-block reservoirs.

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Damage mechanism and plug removing technique of the low permeability reservoirs in Chunliang Oilfield

JIA Jianghong; CHENG Yuanfang; ZHAO Xiuta; QU Zhanqing; FENG Weiqiang and FENG Puyong

, 2008, 35(3): 1607-0.

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Most reservoirs in the Chunliang Oilfield are low permeability reservoirs characterized by multiple oil layers, thin single layer, poor physical property, complex lithology and serious aeolotropy. They are seriously damaged during drilling, completion, production, water injection and well repairing, as a result, the injection-production pressure difference is high and the single-well oil production low. The key factors causing the formation damage are reservoir property, external fluid and unreasonable stimulation. A low-damage, comprehensive plug-removing agent (CJD-1) is developed based on the formation characteristics and the damage mechanism. Laboratory test and field application show that the agent has good efficiency of relieving blocking, deep penetration and low damage to rock skeletons. It was applied to 9 oil wells and 10 water wells with success ratio of 100%. According to the statistics, the average validity period is over 200 d, the average single-well incremental oil is 481.3 t, and the average incremental injection of individual water well is 7 441.2 m3 during the period of validity.

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Influence of hydrolyzed polyacrylamide on the foam capability of α-Olefin Sulfonate surfactant

WANG Dongmei; HAN Dakuang; XU Guanli and YANG Li

, 2008, 35(3): 1608-0.

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This paper studies the influence of hydrolyzed polyacrylamide (HPAM) on the α-Olefin Sulfonate (AOS) foaming and the foam stability. Hydrolyzed polyacrylamide added into the AOS solution can increase the surface tension of the system as well as its viscosity. From the gas-flow method, the optimal AOS concentration should be 0.1% when the biggest foam volume and the most stability are obtained. The research also shows that HPAM improves the foam stability only by increasing the system viscosity, when the system viscosity being the same, the molecular weight of hydrolyzed polyacrylamide has little influence on the foam capability.

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Current situation and measures of water injection in Chang 8 Layer, Xifeng Oilfield, Changqing

WANG Xiaolin; WU Pingcang; HAN Yaping; LIN Guangrong; SHAO Chuangguo and XU Zhenfeng

, 2008, 35(3): 1609-0.

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To understand the reason why the initial injection pressure is high and the normal injection pressure increases rapidly in the Chang 8 layer, this paper analyzes the mineral composition, clay mineral type and content, pore structure, formation sensitivity, wettability, water chemistry, and injection water quality of the reservoirs. The high initial injection pressure results from tight reservoirs, fine pores and middle-oil wetting; the core injecting water experiment reveals that the middle degree water sensitivity and the scale of BaSO4 and CaCO3 caused by the blending of formation water and injecting water are the main reasons for the formation damage and the rapid pressure increase. The analysis of influences of different injection procedures on the water-injecting pressure shows that the perforation-hydraulic fracturing procedure is the most useful technique to keep pressure constant and the treating diameter of anti-swallowing and plugging removing should be bigger than 4 meters. Recovery waste water reinjection is advantageous to maintaining the water-injection pressure stability.

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Generation mechanism and control measures for H2S in oil wells, Liaohe Oilfield

WANG Qian

, 2008, 35(3): 1610-0.

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H2S may be generated by reactions of sulphur-alcohol and sulfoether in the crude oil or by the sulfur-bearing minerals in the formation at high temperatures. Sulphate can also be reduced to H2S by the sulphate-reducing bacteria in formation water at formation conditions. Experiments show that temperature is the key external factor affecting the formation of H2S. Temperature being over 100 ℃, the content of H2S increases by about 0.03% every 20 ℃ increase in temperature. The content of H2S increases rapidly with temperature being between 160 ℃ and 180 ℃. When temperature is higher than 180 ℃, the speed of H2S generation decreases obviously. With surfactants and mixed additives added, the release of H2S can be prohibited. With the adding of acid chemicals, the content of H2S will increase. H2S in oil wells can be basically eliminated in some time with self-developed H2S remover added.

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Application of facies-controlled modeling technology to the fault-block A11 in A'nan Oilfield

ZHANG Shujuan; SHAO Longyi; SONG Jie; LIU Dating; CHEN Guosheng and REN Chunling

, 2008, 35(3): 1611-0.

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The fault-block A11 in the A'nan Oilfield of the Erlian basin is now at a high water-cut period, and its reservoir heterogeneity has severely affected development results. In order to accurately describe the reservoir and its through-going characteristics, this paper establishes the structural model, the sedimentary microfacies model and the microfacies-controlled property model step by step using facies-controlled modeling technology with multiple stochastic modeling methods and on the basis of study results on seism, logging, geology and development performance. The comparison between facies-controlled modeling and non-facies-controlled modeling reveals that the facies-controlled property model is more reliable in describing reservoir heterogeneity. The successful application in the A'nan Oilfield shows that the facies-controlled modeling technology can satisfactorily characterize the properties of the reservoirs with quick-change sedimentary microfacies and severe heterogeneity, providing dependable geological model for the later development adjustment of oil and gas fields.

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Temperature analysis of electric heating hollow sucker rods and its application

WANG Liying; LI Qitang; LIN Jianping and WANG zhibin

, 2008, 35(3): 1612-0.

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Based on the theories of skin effect and the coupling of electromagnetic and temperature fields, a temperature model of alternating current heating hollow sucker rod was established by the finite element method. The temperature of inner wall and outer wall of hollow sucker rod was simulated, and the factors affecting the temperature distribution were analyzed. There exits a functional relationship among the temperature distribution, the current frequency and the heating time: the higher the frequency, the higher the temperature; the longer the heating time, the higher the temperature. By changing the alternating current frequency and the heating time, the hollow sucker rod temperature can be controlled to suit for the exploition of different kinds of heavy oil. An example was given to show that the hollow sucker rod temperature analysis can be used to estimate the preheating time during the heavy oil recovery, providing reasonable reference for selecting the current frequency and the heating time.

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Full scale test of ZXCY-Series linear motor pumping unit

GU Yuhong; XIAO Wensheng; ZHOU Xiaoxi; ZHANG Shichang and JIN You-hai

, 2008, 35(3): 1613-0.

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To solve the technical problem of the great propulsion permanent magnet synchronous linear motor, the ZXCY-Series linear motor pumping unit is developed. The linear motor pumping unit takes electric energy into straight reciprocating motion directly by frequency conversion and control, and simplifies the energy transfer process. Compared with the beam pumping unit, its energy transfer efficiency is increased by about 23%. The new pumping unit actualizes swabbing parametric stepless adjustment and meets operation requirements during production. It was applied to six wells in Huabei Oilfield, Jianghan Oilfield, Tarim Oilfield and Dagang Oilfield. The average liquid production per day of oil well, the system efficiency of single well, input power, comprehensive power-saving rate all show significant improvement after using the new pumping unit. The pumping unit can meet the needs of deep-pumping wells with the big pump and liquid-raising wells with a high pumping rate, and the needs of such production wells as heavy oil wells and high gas-oil ratio wells and the wells of being short of liquid feed.

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A new computational method for biogenic gas resources

YANG Yuqi; WANG Zhenping; KONG Lingfang; ZHANG Xiangchun and LIU Lei

, 2008, 35(3): 1614-0.

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The widely used method for calculating biogenic gas resources is: through the simulation, the biogas production rate of source rock is determined; the calculation principle similar to volume method is used to estimate the biogas production. There are two disadvantages in this method: under the experimental conditions, the experimental gas production rate is used to represent the actual gas production rate; it is difficult to determine the type of the hydrocarbon source rock by comparing it with experimental samples. From the generation and influencing factors of biogas, this paper quantifies some important factors influencing the biogas generation and determines five elements in the quantificational computing method of biogenic gas which are organic component factor, redox environmental factor, collection coefficient, temperature coefficient, and ultimate gas-forming rate. It also analyzes the quantificational computing method and influencing factors of each parameter. The method was applied to the Fangzheng fault depression and the biogas resource in different layers was calculated.

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Petroleum geology and resources in West Africa：An overview

LIU Jianping; PAN Xiaohua; MA Jun; TIAN Zuoji; CHEN Yongjin and WAN Lunkun

, 2008, 35(3): 1615-0.

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The passive continental margin of West Africa is becoming an attractive area for hydrocarbon exploration, and it experienced four tectonic stages, i.e. pre-rift, syn-rift, transitional and post-rift (drifting) stages. The syn-rift and post-rift stages deposited deep lacustrine hydrocarbon sources and marine hydrocarbon sources of anoxic sediment, respectively, and the transitional stage deposited very thick evaporate rocks, which are very important for forming large traps. The outer basins in the passive margin are the main hydrocarbon-producers in West Africa. Several large rivers formed huge deltas and turbid fans such as Niger Delta, Congo Fan, Kwanza Fan, which contributed large amount of petroleum. Niger Delta and Lower Congo Basin are the most attractive areas in West Africa; Gabon Basin and Rio Muni Basin's remained hydrocarbon resources are limited and the key problem is to find new targets; the exploration in the Kwanza Basin's deep sea is rare and has a certain risk.

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, Volume 35 Issue 3