Productivity Analysis Method of Abnormal High-Pressure Gas Reservoir in Ying-Qiong Basin

Ying-Qiong Basin in the west of South China Sea contains plenty of abnormal high-pressure gas reservoirs, whose stress sensitivity is crucial for well productivity. To explore the influence of stress sensitivity on production, the variable outlet back pressure stress sensitivity experiments were applied to test core sample permeability under different burden pressure and obtain the relational expression of power function of core stress sensitivity. Afterwards, new productivity equation is deduced in consideration of reservoir stress sensitivity, and the affection of stress sensitivity on production is analyzed. The result demonstrates close link between stress sensitivity and productivity, since single well production decreases dramatically when reservoir stress sensitivity has been taken into account. This research is constructive for well-testing data interpretation in stress sensitive gas reservoirs.

Heterogeneity and influencing factors of marine gravity flow tight sandstone under abnormally high pressure:A case study from the Miocene Huangliu Formation reservoirs in LD10 area,Yinggehai Basin,South China Sea

The characteristics of reservoir heterogeneity of the marine gravity flow tight sandstone from the Miocene Huangliu Formation under abnormally high pressure setting at LD10 area in Yinggehai Basin are studied,and the influencing factors on reservoir heterogeneity are discussed,based on modular formation dynamics test,thin sections,XRD analysis of clay minerals,scanning electron microscopy,measurement of pore throat image,porosity and permeability,and high pressure Hg injection,as well as the stimulation of burial thermal history.The aim is to elucidate characteristics of the heterogeneity and the evolution process of heterogeneity of the reservoir,and predict the favorable reservoirs distribution.(1)The heterogeneity of the reservoir is mainly controlled by the cement heterogeneity,pore throat heterogeneity,quality of the reservoir heterogeneity,and the diagenesis under an abnormally high pressure setting.(2)The differences in pore-throat structure caused by diagenetic evolution affected the intergranular material heterogeneity and the pore throat heterogeneity,and finally controlled the heterogeneity of reservoir quality.(3)Compared with the reservoir under normal pressure,abnormally high pressure restrains strength of the compaction and cementation and enhances the dissolution of the reservoir to some extent,and abnormally high pressure thus weakening the heterogeneity of the reservoir to a certain degree.The favorable reservoirs are mainly distributed in the gravity flow sand body under the strong overpressure zone in the middle and lower part of Huangliu Formation.

Test and Study of the Rock Pressure Sensitivity for KeLa-2 Gas Reservoir in the Tarim Basin

KeLa-2 gas reservoir is the largest uncompartimentalized gas field so far discovered in China, with a reserve of hundreds of billions of cubic meters of dry gas. It has such features as extremely long interval (550m), high pressure (74.5MPa) and pressure coefficient (2.022). Gas reservoirs with a pressure coefficient of over 2.0 are not commonly found. The abnormal high-pressure reservoirs are quite different in characteristic and performance during the process of depletion exploitation. Therefore, it is necessary to know the property of pressure sensitivity for this abnormal high-pressure reservoir. The aim of this paper is to test the reservoir pressure sensitivity and to analyze its effect on the deliverability of gas. Through some experiments, the permeability change with the confining pressure of rock samples from KeLa-2 abnormal high-pressure gas reservoir is measured. A power function is used to match the measured data, and to derive an empirical equation to describe the change of permeability through the change of the reservoir pressure or effective overburden pressure. Considering the permeability change during the development of reservoirs, a conventional deliverability equation is modified, and the deliverability curve for KeLa-2 gas reservoir is predicted. The research indicates that the extent of the pressure sensitivity of rock samples from KeLa-2 is higher than that from the Daqing oilfield. KeLa-2 reservoir rock has the feature of an undercompaction state. The pressure sensitivity of a reservoir may decrease the well deliverability. It is concluded that for KeLa-2 reservoir the predicted absolute open flow (AOF), when the pressure sensitivity is taken into account, is approximately 70% of the AOF when permeability is constant and does not change with pressure.

Action mechanisms of abnormal fluid pressure on physical properties of deep reservoirs: A case study on Jurassic Toutunhe Formation in the southern margin of Junggar Basin, NW China

Considering the action mechanisms of overpressure on physical changes in skeleton particles of deep reservoir rocks and the differences in physical changes of skeleton particles under overpressure and hydrostatic pressure, the sandstone of the Jurassic Toutunhe Formation in the southern margin of Junggar Basin was taken as an example for physical modeling experiment to analyze the action mechanisms of overpressure on the physical properties of deep reservoirs. (1) In the simulated ultra-deep layer with a burial depth of 6000-8000 m, the mechanical compaction under overpressure reduces the remaining primary pores by about a half that under hydrostatic pressure. Overpressure can effectively suppress the mechanical compaction to allow the preservation of intergranular primary pores. (2) The linear contact length ratio under overpressure is always smaller than the linear contact length ratio under hydrostatic pressure at the same depth. In deep reservoirs, the difference between the mechanical compaction degree under overpressure and hydrostatic pressure shows a decreasing trend, the effect of abnormally high pressure to resist the increase of effective stress is weakened, and the degree of mechanical compaction is gradually close to that under hydrostatic pressure. (3) The microfractures in skeleton particles of deep reservoirs under overpressure are thin and long, while the microfractures in skeleton particles of deep reservoirs under hydrostatic pressure are short and wide. This difference is attributed to the probable presence of tension fractures in the rocks containing abnormally high pressure fluid. (4) The microfractures in skeleton particles under overpressure were mainly formed later than that under hydrostatic pressure, and the development degree and length of microfractures both extend deeper. (5) The development stages of microfractures under overpressure are mainly controlled by the development stages of abnormally high pressure and the magnitude of effective stress acting on the skeleton particles. Moreover, the development stages of microfractures in skeleton particles are more than those under hydrostatic pressure in deep reservoir. The multi-stage abnormally high pressure plays an important role in improving the physical properties of deep reservoirs.

Progress and development directions of stimulation techniques for ultra-deep oil and gas reservoirs

By reviewing the development history of stimulation techniques for deep/ultra-deep oil and gas reservoirs,the new progress in this field in China and abroad has been summed up,including deeper understanding on formation mechanisms of fracture network in deep/ultra-deep oil and gas reservoir,performance improvement of fracturing fluid materials,fine stratification of ultra-deep vertical wells,and mature staged multi-cluster fracturing technique for ultra-deep and highly deviated wells/horizontal wells.In light of the exploration and development trend of ultra-deep oil and gas reservoirs in China,the requirements and technical difficulties in ultra-deep oil and gas reservoir stimulation are discussed:(1)The research and application of integrated geological engineering technology is difficult.(2)The requirements on fracturing materials for stimulation are high.(3)It is difficult to further improve the production in vertical profile of the ultra-deep and hugely thick reservoirs.(4)The requirements on tools and supporting high-pressure equipment on the ground for stimulation are high.(5)It is difficult to achieve efficient stimulation of ultra-deep,high-temperature and high-pressure wells.(6)It is difficult to monitor directly the reservoir stimulation and evaluate the stimulation effect accurately after stimulation.In line with the complex geological characteristics of ultra-deep oil and gas reservoirs in China,seven technical development directions are proposed:(1)To establish systematic new techniques for basic research and evaluation experiments;(2)to strengthen geological research and improve the operational mechanism of integrating geological research and engineering operation;(3)to develop high-efficiency fracturing materials for ultra-deep reservoirs;(4)to research separated layer fracturing technology for ultra-deep and hugely thick reservoirs;(5)to explore fracture-control stimulation technology for ultra-deep horizontal well;(6)to develop direct monitoring technology for hydraulic fractures in ultra-deep oil and gas reservoirs;(7)to develop downhole fracturing tools with high temperature and high pressure tolerance and supporting wellhead equipment able to withstand high pressure.

Numerical Simulation of Oil and Gas Two-Phase Flow in Deep Condensate Gas Reservoirs in Bohai Buried Hills

The BZ19-6 gas field is characterized by high temperature and high pressure (HTHP), high condensate content, little difference between the formation pressure and dew point pressure, and large amount of reverse condensate liquid. During the early stage of depletion development, the production gas-oil ratio (GOR) and production capacity remain relatively stable, which is inconsistent with the conventional reverse condensate seepage law. In view of the static and dynamic conflict in development and production, indoor high-temperature and high-pressure PVT experiment was carried out to reveal the mist-like condensation phenomenon of fluids in the BZ19-6 formation. And the seepage characteristics of condensate gas reservoirs with various degrees of depletion under the condition of HTHP were analyzed based on production performance. The change rule of fluid phase state was analyzed in response to the characterization difficulties of the seepage mechanism. The fluid state was described using the miscible mechanism. And the interphase permeability interpolation coefficient was introduced based on interfacial tension. By doing so, the accurate characterization of the “single-phase flow of condensate gas-near-miscible mist-like quasi single-phase flow-oil-gas two-phase flow” during the development process was achieved. Then the accurate fitting of key indicators for oilfield development was completed, and the distribution law of formation pressure and the law of condensate oil precipitation under different reservoir conditions are obtained. Based on research results, the regulation strategy of variable flow rate production was developed. Currently, the work system has been optimized for 11 wells, achieving a “zero increase” in the GOS of the gas field and an annual oil increase of 22,000 cubic meters.

Origin of abnormal high pressure and its relationship with hydrocarbon accumulation in the Dina 2 Gas Field, Kuqa Depression

Based on distribution of formation pressure by indirect estimation and formation testing,this study investigates origin of abnormal high pressure in the Dina 2 Gas Field in the Kuqa Depression in combination with the latest research findings.Contribution of major overpressure mechanisms to this gas field is estimated,and generation of the abnormal high pressure as well as its relationship with natural gas accumulation is explored.Disequilibrium compaction,tectonic stress,and overpressure transfer are the major overpressure mechanisms.Overpressure transfer resulted from vertical opening of faults and folding is the most important cause for the overpressure.Gas accumulation and abnormal high pressure generation in the reservoirs of the Dina 2 Gas Field show synchroneity.During the early oil-gas charge in the Kangcun stage,the reservoirs were generally normal pressure systems.In the Kuqa deposition stage,rapid deposition caused disequilibrium compaction and led to generation of excess pressure(approximately 5-10 MPa)in the reservoirs.During the Kuqa Formation denudation stage to the Quaternary,reservoir overpressure was greatly increased to approximately 40-50 MPa as a result of vertical pressure transfer by episodic fault activation,lateral overpressure transfer by folding and horizontal tectonic stress due to intense tectonic compression.The last stage was the major period of ultra-high pressure generation and gas accumulation in the Dina 2 Gas Field.

Gas expansion caused by formation uplifting and its effects on tight gas accumulation:A case study of Sulige gas field in Ordos Basin,NW China

Gas expansion caused by significant exhumation in the Sulige gas field in the Ordos Basin since Late Cretaceous and its effects on hydrocarbon accumulation have been investigated systematically based on comprehensive analysis of geochemical,fluid inclusion and production data.The results indicate that gas volume expansion since the Late Cretaceous was the driving force for adjustment and secondary charging of tight sandstone gas reservoirs in the Sulige gas field of the Ordos Basin.The gas retained in the source rocks expanded in volume,resulting in gas re-expulsion,migration and secondary charging into reservoirs,while the gas volume expansion in the tight reservoirs caused the increase of gas saturation,gas-bearing area and gas column height,which worked together to increase the gas content of the reservoir and bring about large-scale gas accumulation events.The Sulige gas field had experienced a two-stage accumulation process,burial before the end of Early Cretaceous and uplifting since the Late Cretaceous.In the burial stage,natural gas was driven by hydrocarbon generation overpressure to migrate and accumulate,while in the uplifting stage,the gas volume expansion drove internal adjustment inside gas reservoirs and secondary charging to form new reservoirs.On the whole,the gas reservoir adjustment and secondary charging during uplifting stage is more significant in the eastern gas field than that in the west,which is favorable for forming gas-rich area.

准噶尔盆地深层-超深层碎屑岩致密气储层特征及其控制因素

为寻找准噶尔盆地深层-超深层有利碎屑岩致密气储层,利用钻井、录井、薄片及化验资料,研究了碎屑岩致密气储层发育特征、储集空间类型、物性变化特征及有利储层控制因素。研究结果表明:①深层-超深层有利碎屑岩致密气储层储集岩主要为三角洲砾岩和砂岩,以细砾(砂)岩、中砾(砂)岩及中-细砾(砂)岩为主,为岩屑类砂岩。砾石成分和砂岩岩屑以凝灰岩为主,胶结物主要为方解石,局部富集沸石类。②储集空间为孔隙和裂缝,以孔隙为主。储集空间有孔隙型、裂缝型和孔隙-裂缝混合型3种组合类型。孔隙主要为原生剩余孔隙和次生溶蚀孔隙,以次生溶蚀孔隙为主。裂缝以成岩压实微裂缝和构造裂缝为主。③碎屑岩致密气储层垂向上形成了3个次生孔隙发育带。④岩石成分、建设型成岩作用和异常高压是控制有利储层的主要因素,3个主要因素控制了盆地深层-超深层碎屑岩致密气有利储层的发育和分布。

岩矿扫描录井在碳酸盐岩储层异常高压预测中的应用

做好碳酸盐岩储层异常高压随钻预测,是降低溢流、井漏风险发生概率的关键。针对塔里木盆地富满地区一间房-鹰山组碳酸盐岩储层异常高压预测难题,通过岩矿扫描录井技术,获取与断控缝洞型碳酸盐岩储层异常高压相关的孔隙度、裂缝数两个参数,引入反映裂缝复杂程度的裂缝复杂指数,并建立孔隙度与裂缝复杂指数图板,对塔里木盆地富满地区一间房-鹰山组碳酸盐岩储层异常高压进行识别和预测。以塔里木盆地富满地区FD 1井为例,应用孔隙度与裂缝复杂指数图板能有效表征碳酸盐岩储层异常高压段,为该地区碳酸盐岩储层异常高压研究和预测提供了一个新方法,也为下一步勘探开发提前采取工程措施,降低溢流、井漏风险发生概率提供技术支撑。

应力敏感特低渗气藏绝对无阻流量计算新方法

为准确评价特低渗气藏产能,推导考虑应力敏感效应的气井产能方程,建立了特低渗气藏绝对无阻流量计算新方法。通过产能方程左端项数值与产气量的线性关系,确定方程系数A和B,建立考虑应力敏感效应的气井产能方程和绝对无阻流量计算公式,提高特低渗气藏产能预测精度。经S气藏A1、B1、B2井现场应用,相比于忽略应力敏感影响,应力敏感的气井绝对无阻流量下降19%,设计产能精度达到90.4%和95.0%,表明应力敏感效应对气井产能影响较大。新方法更适用于特低渗气藏的产能评价,具有较大的推广应用价值。

西湖凹陷古近系致密砂岩气“三元耦合控藏”特征

针对西湖凹陷古近系致密砂岩气成藏机制与成藏模式尚不明确等问题,综合分析了烃源岩的特征与生排烃期次,研究异常高压的成因与分布特点,以及大型储集体的展布与物性特征,建立了致密砂岩气的成藏模式。研究结果表明:烃源岩、异常高压和致密储层“三元耦合控藏”是西湖凹陷致密砂岩气藏成藏关键因素,其中古近系煤系烃源岩条件优越,生气高峰期与储层致密形成时间一致,生烃增压同时提供了富厚的物质基础;异常高压改善储层物性,同时利于致密砂岩气的长距离运移和聚集;大规模的砂岩储集体发育,致密砂岩气在异常高压作用下汇聚成藏。西湖凹陷致密砂岩气藏呈现出“自源侧向-垂向”的成藏模式,共发育“原生型”和“改造型”2类致密砂岩气藏,具有良好的勘探前景。

地层异常高压形成机理的研究

通过对地层中各种不同异常高压形成机理的系统分析 ,认为不同的异常高压形成机理具有不同的作用对象和作用范围 ,不均衡压实、构造挤压、生烃增压和流体热膨胀增压是异常高压形成的主要机理 .不均衡压实增压主要在泥岩或大套泥岩内砂岩中有作用 ,生烃增压则主要发生于成熟—高成熟的烃源岩中 ,流体热膨胀增压主要发生于封闭体系中 ,三者具有一定的普遍性 .构造挤压作用增压主要发生于压性盆地中 ,在前陆盆地山前带具有普遍意义 .流体密度差增压主要发生于油气藏范围 ,主要产生局部异常高压 .矿物成岩作用引起的超压主要发生于储层中 ,仅是辅助的异常高压形成机理 .水压头对某些盆地的超压形成有一定作用 ,缺乏普遍性 .渗透作用对超压意义不大 .实际的含油气盆地中 ,往往是某一种或几种成因占主导地位 ,而其他成因基本不起作用或作用不明显 .所以 。

塔里木盆地异常高压气藏的主要地质特征和成藏模式

在全面论述塔里木盆地异常高压气藏分布的基础上,重点剖析了南天山和西昆仑山的山前坳陷的区域演化、异常高压成因、储气构造形成和成藏期,进而提出其成藏模式,探讨异常高压气藏形成的关键和勘探靶区。库车坳陷除依南2气藏为自源型外,其它5个气藏均属晚期充注型;主成藏期是中新世晚期—上新世早期,背斜发育受一组后展式扩展的逆冲断层控制,更新世以来天然气向原储气构造内充注,异常高压是自源型高压和传导型高压的叠加。叶城凹陷柯克亚背斜深部的古近系在中新世成藏,上新世-早更新世随地层褶皱发生调整,属晚期调整的气藏;浅部的中新统气藏则是晚期充注型,除气源岩供气外还有深部的古近系气藏为之供气,应属晚期次生成藏。

砂岩透镜体成藏的动力学机制

砂岩透镜体的成藏动力学机制是一个还没有完全解决的问题。四周为生烃泥岩所包围的砂体是一个封闭或半封闭的水力系统,烃类如何充注进去而孔隙水又如何被排替出来,就成为问题的关键和难点。在对比岩性和构造圈闭成藏特征的基础上,对泥岩中初次运移的动力和砂体中二次运移相态的转换以及浮力的作用进行了综合研究和动态分析。认为充注的动力主要是异常高压力、毛细管压差、分子扩散和渗透压力;在砂体中油气聚集和排水的动力主要是浮力及其产生的附加压力。这些成藏动力随生烃泥岩热演化阶段的不同,也有所侧重和不同。在低熟阶段主要是压实和渗透水流的充注;在成熟阶段主要是以烃-水两相渗流、毛细管压差和分子扩散等方式进行充注,同时在浮力作用下油气在砂体中开始聚集;在高成熟阶段除继承上述充注方式外,同时又不断有天然气从砂体顶部扩散出来,最终导致砂体中以油相聚集为主。影响砂岩透镜体成藏的地质要素是生烃泥岩的质量、厚度以及砂体的物性和产状。总之,砂岩透镜体成藏要比构造圈闭成藏困难得多。

华北东濮凹陷异常高压与流体活动及其对储集砂岩成岩作用的制约

Basin-Mod软件模拟显示东濮凹陷35Ma左右孔隙流体已出现较高异常压力,综合分析表明欠压实作用是发育异常高压的主要机制。处于异常高压带内的泥岩存在微裂隙带,是异常高压流体压裂的直接结果井可以成为流体运移的通道。通过典型研究区砂岩压实(溶)量、压实-胶结关系、沉积参数-储集物性的对比,表明异常高压流体的确对砂岩的压实作用具有抑制作用。另一方面,自生石英流体包体均一温度大部分在105～145℃之间,频数呈多峰式展布,可能显示幕式流体活动。该温度范围内由于没有有机酸的大规模生成,泥岩频繁发生的幕式流体泄压活动,使得富含CO_3^(2-)的高压流体在注入砂岩(低压区)孔隙后易与Ca^(2+)、Mg^(2+)、Fe^(2+)等离子结合,导致砂岩储层发生强烈的(晚期)碳酸盐沉淀和胶结作用。

异常高压气藏开发特征的解析研究

异常高压气藏开发过程中 ,在视地层压力与累积产量之间的关系曲线上常出现上凸拐点现象 ,正确认识异常高压气藏的开发特征对合理规划异常高压气藏的开发具有十分重要的意义。为了系统研究异常高压气藏的开发特征 ,通过将储层流体及岩石物性参数的变化特征引入圆形封闭气藏数学模型 ,求得了分析异常高压气藏开发特征的平均地层压力解 ,并就物性参数变化对开发特征的影响 ,分析研究了异常高压气藏压力衰竭式开发过程中 ,视地层压力与累积产量关系曲线可能出现的各种特征。流体、岩石、水体等参数变化的敏感性研究结果表明 ,异常高压气藏视地层压力与累积产量之间的关系曲线可以表现为一条直线、或者上 /下凸的曲线等多种可能的形态。为全面认识异常高压气藏的的开发特征提供了一种解析方法 。

异常高压气藏应力敏感性及其对产能的影响

针对异常高压气藏开发实践,利用气体稳定渗流理论,推导得到考虑异常高压气藏应力敏感性的产能方程,并对某异常高压气藏实例井的产能进行了预测,预测效果较好。本次研究提出的产能方程符合异常高压气藏的开发实际,具有重要的指导意义。

山东东营牛庄洼陷沙三中亚段浊积砂体储层特征及影响因素

山东东营牛庄洼陷沙三中亚段浊积砂体储层以长石细砂岩、岩屑细砂岩及粉砂岩为主 ,结构成熟度及成分成熟度均较低。储层微观特征研究表明 ,砂体中发育了剩余原生粒间孔、粘土矿物杂基内的微孔隙、粒间溶孔、粒内溶孔及微裂缝等储集空间类型 ,孔隙结构以低渗细喉型为主 ,为物性较差的中低孔、低渗型储层。通过对储层物性影响因素的研究得出 ,岩石组构、沉积微相、成岩作用和异常超压的形成与分布是影响本区浊积砂体储层物性的主要因素。其中 ,碳酸盐胶结物、硅质胶结物及自生粘土矿物是致使储层物性变差的主要原因 ,沉积物中有机质的大量生烃以及粘土矿物在转化过程中所释放出的酸性水的溶解作用是产生次生孔隙的重要因素 ,而异常超压的存在、高的地温场及烃类的早期进入是部分原生孔隙和次生孔隙得以保存的重要条件。

西湖凹陷平湖构造带平湖组砂岩储层特征及其主控因素

以岩心和铸体薄片观察为基础,结合扫描电镜、储层物性、压汞及试采等综合资料分析,对西湖凹陷平湖构造带平湖组砂岩储层发育特征进行了研究。结果表明,该区平湖组储层岩石类型以长石质石英砂岩为主,颗粒分选和磨圆度较好,成分成熟度中等,结构成熟度高;储层物性表现为低孔、低渗和中孔、中渗的特征,孔、渗相关性好;孔隙类型主要发育有粒间溶孔和剩余原生粒间孔,喉道类型以缩颈型喉道、片状喉道、弯片状喉道为主,孔、喉组合以中孔、粗喉为主。在此基础上,从沉积相、成岩作用和异常超压等方面对该区储层发育主控因素进行了分析。综合研究表明,沉积相是该区储层发育的主控因素之一,其中三角洲平原分支河道砂体物性最好,其次为三角洲前缘水下分流河道砂体;压实作用和胶结作用导致该区储层物性变差,溶蚀作用则有助于形成次生孔隙空间,并大大改善储层物性;异常超压对研究区储层有建设性影响,可以在一定程度上使原生孔隙得以保存,并促进早期碳酸盐胶结物的溶解,形成粒间溶孔,改善储层物性。