The generation kinetics of natural gases in the Kela-2 gas field from the Kuqa Depression, Tarim Basin, northwestern China

The Kela-2 gas field, found in the Kuqa Depression of the Tarim Basin, northwestern China, is a large-sized dry gas field (C1 /C1-5 =0.992 0.999) and characterized by ultra-high pressure (pressure factor up to 2.0 2.2). The pyrolysis experiment was carried out under isothermal gold-tube closed system, with samples collected from the Jurassic coal, Jurassic mudstone and Triassic mudstone in the Kuqa Depression. The result of gas yield showed that the Middle and Lower Jurassic source rocks have higher gas generation potential than the Triassic source rocks. The kinetic modeling of gas generation and methane carbon isotope fractionation suggested that the Kela-2 gases belong to the products of high-over mature stages and were mainly derived from the Middle and Lower Jurassic coal-bearing strata. The Triassic source rocks made a minor contribution to the Kela-2 gases. The Kela-2 gases chiefly generated from coal-bearing source rocks with R o values from 1.3% to 2.5%, and thus primarily accumulated after 5 Ma.

Geochemical characteristics and formation process of natural gas in Kela 2 gas field

On the basis of a large amount of natural gascomponents and the carbon isotope as well as some otheranalysis data in Kela 2 gas field, the geochemical character-istics, source, origin, and formation process of natural gashave been discussed. The components of gas in the field tendto be 'dry', and the drying coefficient is close to 1.0. Thecarbon isotope tends to be heavier, for instance, the averageof δ13C1 is -27.36‰ and that ofδ13C2 is -18.5‰. Compre-hensive analysis shows that humic natural gas in the Kuqapetroleum system comes mainly from Triassic and Jurassicsource rocks, and the contribution of Jurassic source rocks tothe pool maybe is more than that of Triassic rocks. The maincause that the gas tends to be dry and bears heavier isotopecomposition lies in the fact that Kela 2 natural gas is the ac-cumulation of late production of humic source rocks, and itis affected by the abnormal high pressure as well. Consider-ing the hydrocarbon generating and structural history, wecan regard the gas pool formation processes as twice fillingand twice adjusting （destroying）, that is, the filling anddestroying process in the early Himalayan movement and thefilling and adjusting in the late Himalayan movement.

Thermodynamic conditions of framework grain dissolution of clastic rocks and its application in Kela 2 gas field

Feldspar and clastic debris are the most important constituent framework grains of sedimentary clastic rocks and their chemical dissolution plays an essential role in the formation and evolution of the secondary pore in the reservoir rocks. On the basis of thermodynamic phase equilibrium, this study investigates the chemical equilibrium relationships between fluid and various plagioclase and K-feldspar in diagenesis of the sediments, particularly, the impact of temperature and fluid compositions (pH, activity of K+, Na+, Ca2+ and so on) on precipitation and dissolution equilibria of feldspars. Feldspar is extremely easily dissolved in the acid pore water with a low salinity when temperature decreases. The dissolution of anorthite end-member of plagioclase is related to the Ca content of the mineral and the fluid, higher Ca either in the mineral or in the fluid, easier dissolution of the feldspar. Moreover, the dissolution of albite end-member of plagioclase is related to Na of both the mineral and fluid, lower Na out of both the mineral and fluid, easier dissolution of the mineral. Similarly, lower-K fluid is more powerful to dissolve K-feldspar than the higher. The anorthite component of plagioclase is most easily dissolved in ground water-rock system, the albite is the secondary, and K-feldspar is the most stable. Selective dissolution of plagioclase occurs in diagenesis because of the plagioclase solid solution that is mainly composed of albite and anorthite end-members, Ca-rich part of which is preferentially dissolved by the pore water, in contrast to the Na-rich parts. Based on investigation of reservoir quality, secondary pore, dissolution structures of feldspar, clay minerals and ground water chemistry of the Kela 2 gas field of Kuqa Depression in the Tarim basin of Western China, we discovered that the secondary pore is very well developed in the highest quality section of the reservoir, and the plagioclase of which was obviously selectively dissolved, in contrast to the overgrowth of K-feldspar. Chemistry of the ground water out of the highest quality section of the reservoir is consistent with the complete dissolution field of anorthite, partial dissolution field of albite component of plagioclase, and the precipitation of K-feldspar on the temperature-logK phase equilibrium diagram drawn from this study. The thermodynamic modeling calculation gave us an insight into formation of the secondary pore within the reservoir, and the dissolution of plagioclase an important cause of the secondary pore. It is assumed that the solvent to dissolve the plagioclase frame grains originated from the origin-enriched compacted fluid acids out of the mudstone buried beneath the top of geopressured zones in the Kuqa Depression.

Geological analysis and physical modeling of structural pumping in high effective formation of Kela 2 gas field

In a 3-D closed geological body, in case “structural expanding” inside is induced by stress, it can produce the pressure difference between the expanding cell and surrounding rock, then generate a pumping force directed toward the cell and accelerate the directional flow of fluid in the strata. The structural style and conditions of gas reservoir-formation in the Kuqa depression are favorable to the structural pumping. According to similarity principle, a physical modeling of structure formation and gas filling process of the Kela 2 gas field has justified the occurrence of structural pumping and its important role in gas-reservoir formation with high efficiency under the compressive and well-sealed circumstance. Therefore, authors propose that structural pumping is an important mechanism of gas reservoir-formation with high efficiency in the Kuqa depression.

Migration and accumulation of natural gas in Kela-2 gas field

With the guidance of petroleum system theory,the dynamic filling history of natural gas in the Kela-2 gasfield is analyzed by using a large suite of oil and gas geo-chemistry evidence in combination with the tectonic evolu-tion history and reservoir evolution history. It concludes thatthe Kela-2 gas field was formed by capturing the gas gener-ated during the main gas generation period, while the latekerogen cracking gas contributed a little to the gas field. Itsuggests that the gas generated during the main gas genera-tion accumulated in the early-formed wide-gentle anticline,which is the necessary condition for natural gas to re-migrateand enrich late to form the large-scale gas reservoir. Thenewest research shows that the filling history of gas in theDabei-1, Yinan-2, Tuziluoke and Dina-2 gas fields was re-lated with the natural gas accumulation in the early wide-gentle anticline as well as late re-migration and enrichmentof natural gas.

Control factors and porosity evolution of high-quality sandstone reservoirs of Kela-2 gas field in Kuqa Depression

By using the integrated methods includingsandbodies modelling of the outcrops, sedimentary facies ofthe cores and well logs of the drilled wells, and the reservoircorrelation of interwells, it is thought that the sandstone res-ervoirs of Kela-2 gas field are a suit of high-quality naturalgas reservoirs with great thickness, extensive and continuousdistribution, high porosity and permeability, and a few bar-rier beds. Sedimentary facies and microfacies are the mainfactors controlling the reservoir distribution and interiorheterogeneity. Based on a great deal of data of rock’s thinsections, porosity, permeability, and the parameters of capil-lary pressure, the reservoir diagenesis, controls, mechanismand evolution of pores have been studied. It is consideredthat compaction in the early stage and diagenetic dolomiteand calcite cements have effect on the decline of reservoirsproperty. Now compaction is chiefly middle to weak. Thebetter reservoirs have no or a few calcite cements. In theearly of deep buried stage, there are still mainly remainderprimary intergranular pores. The authigenic kaolinite ofreservoirs is the production of the dissolution of feldsparsand lithic fragments. The dissolution results in the partlymodified and broadened secondary intergranular pores. Inthe late of deep buried stage, structure fissures and over-pressure were in favor of improving and preservation ofthese pores.

Petroleum geological characteristics of Kela-2 gas field

The Kela-2 gas field is located in the center ofKelasu structural belt in Kuqa Depression. This trap is oneof a series of traps in the folded belts which are distributed ina string of pearls in the dual structure. The primary gas-bearing layers are sandstone of Lower Cretaceous K1bswhile the secondary layers are dolomite member and gluten-ite member of Lower Tertiary E1-2km and sandstone ofLower Cretaceous K1b. The main component of natural gasis methane whose content is higher than 97%. It is charac-terized by dry gas whose source rock is Jurassic coal meas-ure. The Kela-2 structural trap was formed during the Xiyuperiod and then became a reservoir in the late time. The res-ervoir formed late and the thick seal rock of Lower Tertiarygipsmantle are the avail reason why the giant Kela-2 gasfield has been well kept. The abnormal high pressure of theKela-2 gas field results from the strong structural compres-sion in the northern part during the Xiyu period.

Experimental research on reservoir sensitivity to stress and impacts on productivity in Kela 2 Gas Field

Kela 2 Gas Field, with high formation pressure (74.35MPa), high pressure coeffi-cient (2.022) and difficulty of potential test and evaluation, is the largest integrated proved dry gas reservoir in China so far and the principal source for West-East Gas Development Project. In order to correctly evaluate the elastic-plastic deformation of rocks caused by the pressure decline during production, some researches, as the experiment on reservoir sensitivity to stress of gas filed with abnormal high pressure, are made. By testing the rock mechanic properties, porosities and permeabilities at different temperature and pressure of 342 core samples from 5 wells in this area, the variations of petro-physical properties at changing pressure are analyzed, and the ap-plicable inspection relationship is concluded. The average productivity curve with the reservoir sensitivity to stress is plotted on the basis of the research, integrated with the field-wide produc-tivity equation. The knowledge lays a foundation for the gas well productivity evaluation in the field and the gas field development plan, and provides effective techniques and measures for basic research on the development of similar gas fields.

塔里木盆地克拉2气田异常高压的成因分析及其定量评价

塔里木盆地库车坳陷克拉 2气田自始新统以下地层内砂岩储层的实测压力梯度为 1.8～ 2 .1MPa/10 0 m,过剩压力达 30～ 35 MPa,表现为明显的异常高压。前人认为超压的形成主要受控于构造挤压作用 ,此外还有高压天然气的注入、构造抬升等因素 ,基本不存在欠压实作用。本文首先总结了各种成因机制的可能性 ,以此为依据 ,定量评价了气柱浮力、欠压实作用和构造挤压作用等因素对砂岩内异常高压的贡献 ,并提出了克拉 2气田超压形成的概念模式。研究发现 ,该气田不同深度间的过剩压力差异完全是气柱浮力引起的 ,但气柱浮力对超压的贡献不超过 10 % ;明确指出欠压实作用肯定存在 ,且对砂岩中超压的形成起着重要作用 ,其贡献一般为 2 0 %～ 30 % ,部分层段高达 4 0 %～ 5 0 % ;从构造压实作用机理出发 ,分三种情况讨论了构造挤压对流体增压的影响 ,认为构造应力能够传递给流体的最大压力为侧向上的最大主应力与沉积压实阶段的上覆负荷之差 ,其对本地区超压的贡献最大可达 4 0 %～ 5 0 % ,部分层段仅 2 0 %～ 30 %。克拉苏地区超压形成的时间先后顺序 (概念模式 )为 :首先因欠压实作用而出现超压 ,形成了封闭体系 ;其次为天然气的快速注入 ;而康村期 (N1 - 2 k)

异常高压气藏岩石变形特征及其对开发的影响——以克拉2气田为例

克拉 2气田是至今为止在中国陆上找到的最大整装干气气藏 ,也是“西气东输”的主力产气场 ,因此 ,开发好克拉 2气田意义重大而深远。由于该气田地层压力高 (74.3 6 MPa) ,压力系数高达2以上 ,属于异常高压气藏 ,故在衰竭式开采过程中 ,随着气藏的压力下降 ,该气藏的岩石骨架要承受比常规气藏大得多的净上覆压力 ,结果会使岩石发生显著的弹塑性形变和岩石渗透率、孔隙度和岩石压缩系数等物性参数减小 ,从而影响气藏的开发效果 1。据此 ,研究气藏开发过程中岩石形变对产能的影响是一个非常重要的课题。依据岩石覆压实验研究了克拉

库车克拉2气田多期油气充注的古流体证据

对库车前陆盆地克拉2气田储集层进行流体包裹体分析、荧光光谱分析、场发射扫描电镜观察、岩心显微CT扫描及油气地球化学分析,从古流体证据的角度综合研究克拉2气田多阶段油气充注过程。克拉2气田经历了中新世早中期(N1)原油充注、上新世库车组沉积期(N2)高成熟油气充注与破坏、第四系(Q1以来)高—过成熟煤成气充注的3期成藏过程。储集层中广泛分布的残余干沥青、较发育的气液两相烃包裹体、纳米孔中的残余油、现今气层和水层中较高的颗粒(抽提物)荧光指数、储集层岩石较大的热解值等均是早期原油充注的证据;残余干沥青、含沥青的3相烃包裹体、凝析油轻质正构烷烃大量损失、石蜡质和芳烃等重组分含量相对较高、金刚烷含量异常高等均是早期原油遭受气洗发生脱沥青作用的有力证据。

利用分形几何定量评价克拉2气田裂缝

根据断层与构造裂缝存在的关系,利用分形几何方法处理断裂系统,并结合测井解释结果建立分维值大小与裂缝密度的对应关系,对古近系库姆格列木群白云岩段、下白垩统巴什基奇克组第二、第三岩性段顶面断层进行分形统计,建立井点断层分维值与裂缝线密度的关系,在此基础上对井间裂缝分布进行了预测。研究认为,断层分维值随着断层密度、延伸长度的增加而增大,井点处断层分维统计值与测井解释得到的裂缝线密度呈正相关关系;平面上,裂缝发育受背斜形态影响明显,靠近背斜轴部、断层分维值大于1.25的区域最有利于裂缝发育;A3井附近,3个储层段裂缝发育密度偏大,部分裂缝可能穿透了中间的隔层,造成附近气井出水。研究结果表明,利用分形几何定量评价裂缝对勘探开发方案部署有指导意义,可以用来对油气田裂缝性储层进行评价。

克拉2气田高压气井风险评估

克拉2气田在开发生产过程中,部分单井出现生产套压、技术套压异常升高的现象。针对高压气井环空压力异常问题,塔里木油田在国内首次开展了单井风险评估工作。在借鉴APIRP90中相关技术标准的基础上,参考国际大石油公司高压气井的管理经验,根据克拉2气田单井的实际情况,通过先静态后动态的评估程序完成了克拉2气田单井风险评估。特别是对4口重点井,在动态评估完成后,正常开井生产日增天然气1000×104m3以上,取得了较大的经济效益和社会效益。通过对评估技术和方法的总结,取得了一些高压气井风险评估技术和方法的初步认识,对国内陆上高压、超高压油气田开展类似的风险评估工作具有借鉴意义。

强烈气洗作用导致原油成分变化的定量计算:以库车坳陷天然气藏为例

库车坳陷以产天然气为主,同时产出少量原油和凝析油,油气充注不同步,普遍具有"油早气晚"的特点,晚期大量天然气的侵入,必然对早期聚集的油藏发生改造作用。对气藏中原油成分变化的定量计算和讨论,可为天然气的注入强度定量评价提供直接证据。未遭受气洗的原油,正构烷烃摩尔浓度的对数与相应的碳数呈线性关系,而气洗作用可使轻组分的正构烷烃最先溶解于干气中,并随着天然气继续向前运移,原始油藏中的轻组分正构烷烃大大减少。以此为理论基础,建立了正构烷烃损失的定量计算模型。结果表明克拉2构造原油正构烷烃损失程度最高,平均可达70%左右,大北构造带原油正构烷烃损失程度差异较大,与该地区断块发育有关。气洗作用导致原油正构烷烃减少,而金刚烷、多环芳烃等在天然气中溶解度较低的化合物得以浓缩富集,相对含量大大增加。轻芳烃含量也会随之而增加,原油芳香度增加,石蜡度降低。在模拟实验基础上对气洗程度进行了定量评价,初步估算表明,克拉2构造原油遭受的气洗作用最强,是其他构造带的2～5倍。

克拉2气田异常高压特征及成因

克拉 2气田异常高压的主要特征是 :异常高压储层的顶部存在下第三系巨厚的盐岩、膏泥岩盖层 ,封闭性能良好 ;含气面积大 ,储量高 ;断层对气藏的形成和保存起关键作用。本研究区异常高压形成的主控因素是构造抬升和水平构造挤压应力。喜山晚期构造运动导致地层大幅抬升 ,遭受剥蚀 ,而垂向、侧向上良好的封闭性使得孔隙流体压力得以保存 ;

克拉2异常高压高产气田完井工艺技术研究

克拉2气田是中国目前最大的整装气田,是西气东输的主要气源地,具有异常高压、高产量的特征。在分析克拉2气田首批开发井完井、射孔工艺的基础上,总结了克拉2气田目前完井工艺中取得的成功经验和不完善之处,对下步的完井工艺提出了改进意见,旨在提高克拉2气田的完井工艺水平。其结论对异常高压、高产量气田的完井有一定的指导意义。

克拉2气田储层岩石的应力敏感性及其对生产动态的影响

克拉 2气田是一个异常高压气藏, 压力系数在 2 0以上。在衰竭式开采条件下, 其地层压力降幅可为普通气藏地层压力降幅的 3倍以上, 因此研究储层岩石应力敏感性及其对生产动态的影响意义重大。研究得出, 岩石的应力敏感性特征主要有: 岩石物性对应力的敏感性总体上不大, 其中以孔隙度最小, 渗透率次之, 压缩系数最大; 岩石物性随地层压力的下降而下降; 在同一地层压降下, 岩石物性下降幅度不是渗透率的连续函数, 而是与渗透率分布范围有关, 高渗透率范围, 岩石物性下降幅度小, 低渗透率范围, 岩石物性下降幅度大。研究得出, 克拉 2气田岩石的应力敏感性对其生产动态的影响较小。

塔里木盆地克拉2气田白垩系储层沉积相

克拉 2气田是我国陆上勘探发现的最大整装气田之一 ,它的发现奠定了塔里木盆地作为我国“西气东输”的重要天然气基地的资源基础。克拉 2气田产层主要为下白垩统巴什基奇克组砂岩、老第三系库姆格列木群底砂岩和白云岩 ,其中下白垩统巴什基奇克组砂岩储层厚度为2 2 0 .3～ 2 85 .2m ,孔隙度为 1.1%～ 2 2 .4 % ,平均 12 .83% ;渗透率为 0 .0 0 4× 10 -3 μm2 ～ 1770 .1× 10 -3μm2 ,平均 5 1.4 6× 10 -3 μm2 。砂岩储层以剩余原生粒间孔为主。通过钻井和露头剖面沉积相对比 ,克拉 2气田巴什基奇克组第三段为扇三角洲前缘沉积 ,主要微相有水下分流河道、水下重力流和浅湖等微相 ,岩性以砂砾岩、含砾砂岩和褐色泥岩为主 ;第二段为辫状河三角洲前缘沉积 ,主要有水下辫状河道、河口砂坝和分流间湾等微相 ,以棕褐色中细砂岩夹薄层泥岩为主 ;第一段为辫状河三角洲平原沉积 ,主要有远端辫状河道和分流间湾微相 ,以棕褐色中细砂岩为主。巴什基奇克组沉积时期 ,古气候以干旱炎热为主 ,北部发育多个扇体 ,在平面上相互连接、叠置而形成多个物源出口 ,形成了一系列由辫状河道组成的辫状河三角洲 ,而非单一辫状河流形成的沉积体 ,从而形成大面积分布的稳定砂体。沉积微相对比表明 ,巴什基奇克组储层是由互相切?

克拉2气田的发现及勘探技术

克拉2气田探明天然气地质储量达2840.29×10~8m^3,是库车山前逆冲带富含油气的实践证明。它的发现是多年来石油地质研究和勘探技术攻关的结果,从而促进了对库车坳陷石油地质规律的认识,有效地指导了库车坳陷的油气勘探,形成了山前超高压气藏的配套勘探技术,基本解决了山前油气勘探的主要难题,库车坳陷勘探程度低,圈闭多,资源量大,油气勘探大有潜力。

库车坳陷克拉2气田异常流体压力演化史

根据克拉2气田现今实测地层压力分析了异常高压发育的特征,并通过流体包裹体测试求取包裹体形成时期的古压力。计算结果表明:下白垩统和古近系库姆格列木群砂岩储层在距今8～6Ma(康村组沉积期末)时,古压力系数大致为1.09～1.18,发育过剩压力为4.6～9.6MPa的异常高压。在此基础上,以古、今压力数据为约束条件,利用数值模拟技术定量恢复出下白垩统与侏罗系异常流体压力的演化历史。研究发现:下白垩统储层流体压力经历了沉积型异常流体压力形成发展(白垩纪-库车组沉积期末)和沉积型异常流体压力萎缩—构造挤压型异常流体压力孕育(库车组沉积期末至今)两个阶段。康村组沉积早期沉积型超压开始出现,库车组沉积期末达到顶峰,过剩压力达40～50MPa;此后,在沉积型超压萎缩—构造挤压型超压孕育过程的耦合下,过剩压力曾降至25～30MPa,更新世起超压略有升高。侏罗系流体压力演化较为简单,吉迪克组沉积期开始出现超压,至库车组沉积期末达到高峰,此后异常高压逐渐萎缩。在克拉2气田的主要成藏时期(距今3～1Ma),烃源岩较储层具有更高的异常压力,源—储压力差为10～30MPa。