Research advances,geological implication and application in Ordos Basin of the “pore-size controlled precipitation” in diagenesis of carbonate rock reservoir

Based on the discovery of pore-size controlled mineral precipitation and cementation heterogeneity in carbonate rock reservoirs,the state of art and the geological implications are summarized,referring to the fluid-rock interaction and chemical hydrodynamics in porous media. (1)The pore-size controlled precipitation phenomenon is common in geological environments,as shown by the heterogeneous cementation and eventual features that the large pores are filled while small pores can be preserved. Related studies are mainly divided into three aspects,including pore structure observations at different scales,numerical simulation of fluid-rock interaction and mineral precipitation experiment. (2)The kinetic models related to surface chemistry can be used to explain the heterogeneous precipitation affected by pore-size distribution. The larger interfacial tension and mineral crystal curvature in the micropores result in the much higher effective solubility.Thus the fluids in micropores can maintain a higher supersaturation with no minerals precipitation. (3)The pore-size controlled precipitation leads to the selective preservation of micropores. It means that the much larger pores tend to be cement-filled while the smaller pores are preserved in the case of coexistence of pores at different scales. The impacts of cementation types on the overall permeability of rock are different. The pore-size controlled precipitation phenomenon is also worthy of attention in the research of geothermal development and geologic sequestration of carbon dioxide. In the last part, based on the heterogeneous cementation and porosity distribution of the Majiagou Formation in the Ordos Basin,we study the impacts of diagenetic fluids properties,origin and cementation patterns on the evolution of pore structure and high-quality reservoir distribution.The discovery and emphasis of pore-size controlled precipitation is of great theoretical significance to our understanding of the complex fluid-rock interaction process,which provides a new perspective for reservoir diagenesis and pore preservation.     

涪陵页岩气井长水平段漏失井固井技术应用研究

涪陵页岩气井钻井过程中井漏频繁,类型多样,严重影响了工程质量,特别是三开长水平段发生漏失油基钻井液甚至固井时发生漏失,影响了固井质量及后期页岩气的开采。针对长水平段漏失井特点,研究了一系列井眼准备技术、高效纤维隔离液封堵技术、管外浆柱结构优化技术、漏失井固井压稳技术,增强堵漏性能,提高固井质量。随着区域不断地扩大,地质情况复杂多变,提出了下一步的研究方向及建议。     

Dedolomitization and calcite cementation in the Middle Devonian Winnipegosis Formation in Central Saskatchewan,Canada

Limestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the Winnipegosis Formation on the east‐central margin of the Elk Point Basin where the overlying Prairie Evaporite deposits have been removed. This type of crystalline limestone is interpreted as dedolomite, based on petrographic observations. The δ¹⁸O and δ¹³C values of the Winnipegosis dedolomite vary from ?12·8‰ to ?11·9‰ VPDB (Vienna Pee Dee Belemnite) and from ?0·5‰ to +1·7‰ VPDB, respectively; both values are significantly lower than those for the corresponding dolomite. The ⁸⁷Sr/⁸⁶Sr ratios of the dedolomite are significantly higher, between 0·7082 and 0·7087. The spatial distribution and geochemical data of the Winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the Prairie Evaporite anhydrite during the latest Mississippian to the Early Cretaceous when the basin was subjected to uplift and erosion. The Winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite, including the occurrence of dedolomite restricted along fractures and adjacent areas, dolomite patches ‘floating’ in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts. However, the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the Winnipegosis dedolomite. Coarsely to very coarsely crystalline, subhedral to euhedral calcite cement is restricted in the dedolomite. The petrographic features, isotopic compositions and homogenization temperatures, coupled with the burial history of the Winnipegosis Formation, constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during Late Cretaceous to Neogene time. The more negative C‐isotopic signatures of the calcite cement (?5·3‰ to ?2·3‰ VPDB) probably reflect a hydrocarbon‐derived carbon.     

Overpressure preventing quartz cementation? - A reply

Chemical compaction and the relative importance of the pressure dissolution and illite-mica induced dissolution (IMID) models have remained a contentious issue, as is the role played by stress in chemical compaction. This paper offers further support and evidence as discussed in Stricker et al. (2016b), focusing on the reservoir quality of the Triassic Skagerrak Formation sandstones in the high pressure high temperature (HPHT) Central Graben, North Sea. The reply discusses alterative reservoir quality interpretations and comments as raised by Maast (2016). A series of theoretical and experimental studies, as well as field based evidence is presented providing strong support to the important role of stress (e.g. vertical effective stress) during chemical compaction. The evidence leads to the conclusion that the process of chemical compaction is stress and temperature driven and significantly enhanced by clay minerals, playing a catalytic role by increasing the width of diffusion pathway or by modifying the kinetics of the dissolution process.     

Ground-based hyperspectral remote sensing of hydrocarbon-induced rock alterations at cement,Oklahoma

Hydrocarbon seepages bring oil and gas from petroleum reservoirs to the surface, these hydrocarbons can generate various kinds of rock alterations, including bleaching of red beds and mineralogical changes. Satellite and airborne remote sensing techniques have been utilized in the detection of rock alterations and hydrocarbon seepages; however, they have limited resolutions and are unable to map vertical outcrops. Ground-based remote sensing techniques hold great potential to characterize rocks with great precisions and resolutions. This study used ground-based Specim hyperspectral data to detect hydrocarbon-induced rock alterations of the Rush Springs sandstone at the Cement field in southeast Anadarko basin, Oklahoma. Hyperspectral data of outcrops and hand specimens were examined, and spectral angle mapper technique was used to compare spectral similarity between image pixels and reference spectra. Laboratory spectroscopy was used to assist with mineral identification and image classification. Remote sensing data detected bleaching of red beds and carbonate cementation. Combining lithological, spectroscopic, remote sensing and geochemical data, this study built a model for petroleum seepage and related rock alterations, and provided a workflow for employing remote sensing techniques in resource exploration.     

黔北矿区煤层顶板水平井钻井关键技术

煤层气顶板水平井是解决松软煤层煤层气开发的主要途径之一。针对贵州黔北矿区复杂的地质和储层条件,为解决煤层顶板水平井漏失、井眼轨迹控制和固完井困难等问题,开展并形成了以轨迹精细控制为核心,以防漏堵漏、偏心连通和固完井等技术配合的成套黔北矿区煤层顶板水平井钻井关键技术。结合现场钻井实践,成功解决了水平井钻井施工中诸多问题,钻井周期明显缩短,经济效益明显提高。研究成果为贵州煤层气钻井和开发提供了新途径,也为高瓦斯矿井地面治理开辟了新的方向,具有显著的应用和推广价值。     

姬塬地区上三叠统长2油层组高岭石胶结与储层评价

姬塬地区长2油层组次生孔隙在储层砂岩的孔隙构成中比值偏大,成岩作用对储集空间的发育具有明显的控制优势。同时,该区长2油层组高岭石分布是鄂尔多斯盆地中南部较为集中且相对偏高的地区,显示出姬塬地区长2油层组在大气水作用、次生孔隙发育等方面具有特殊性。通过对该区高岭石胶结物含量和分布特征的研究,综合考虑储层物性的平面变化特征、沉积相带、构造高点等影响因素,对有利的储层区块提出了建议。     

砂岩早期核心式碳酸盐胶结作用的成像测井证据

早期碳酸盐胶结作用是库车坳陷新生界浅埋藏河流相砂岩内除机械压实外目前正在进行的主要成岩作用,高分辨率电阻率成像测井资料为研究其特征及成因提供了重要的地球物理证据。在电阻率成像测井图像上,早期碳酸盐胶结物呈圆形、椭圆形或不规则斑块状、葡萄状等形态出现,多数顺层理方向分布,其产状有孤立状或分散状斑块、断续胶结纹层和连续胶结纹层等。它们可以发育于砂岩层顶部或底部,也可以与疏松未胶结或弱胶结砂岩呈互层或夹层状交替分布。早期碳酸盐胶结物的沉淀采取核心式胶结模式,即胶结物首先围绕少数核心沉淀,呈斑块状逐渐向外增生,直至从各个核心生长出来的碳酸盐胶结斑块相互靠近和连生导致砂岩层被完全胶结为止。砂体或砂层被碳酸盐胶结的过程遵循由外向内 (由砂体边缘向砂体中心 )、由高渗透纹层向低渗透纹层、由局部胶结核心向周围孔隙增生的规律.     

文昌A凹陷珠海组储层区域成岩作用特征及定量评价

运用砂岩铸体薄片、扫描电镜、图像分析、孔隙定量分析等资料,研究珠海组深部储层砂岩成岩作用,确定成岩作用横、纵向分布规律;计算成岩参数压实损失的孔隙度和压实率、胶结量、视溶蚀率和溶蚀量,分别对压实作用、胶结作用和溶蚀作用进行定量评价,确定区域成岩作用强度.结果表明:珠海组总体为中等—强压实.其中,凹陷西缘为弱胶结、中等溶蚀;凹陷中心以中等胶结、中等溶蚀为主;南断裂东段下降盘为中等—强溶蚀,珠海组一段和二段为中等—强胶结,珠海组三段为弱—中等胶结;南断裂中段下降盘珠海组一段和二段为中等胶结,珠海组三段为弱胶结,珠海组一段为中等近强溶蚀.     

华北板块南缘寒武系苗岭统碳酸盐岩硬底：缺乏生物扰动背景下的早期海底胶结作用

华北地台南缘寒武系苗岭统碳酸盐岩硬底发育在核形石灰岩和鲕粒灰岩之上,并明显截断下伏的碳酸盐沉积物。本文通过对硬底界面之下颗粒间的放射纤维状方解石胶结物和等厚环边的微晶胶结物分析,表明其形成于早期海底胶结作用,该时期早期胶结区靠近沉积物—水界面,易受潮汐和波浪冲刷而暴露海底,并在持续搅动的高能环境中经历磨蚀和平整,形成硬底。由于硬底形成后几乎没有受到强烈改造和持续生物侵蚀的影响,通常表现出简单、平坦的表面形态。研究区馒头组二段含硬底层段形成于低、高能交替的潮间—潮下水道环境,以微晶方解石为主要的胶结剂沉淀;张夏组含硬底层段形成于台内鲕粒滩高速建造期,以物理化学沉淀和早期海底胶结作用为主。研究区出现的硬底表明,该时期海水化学条件和海底生态环境利于碳酸盐沉积物的早期胶结。硬底作为早期海底胶结作用的突出证据,对于研究碳酸盐沉积物的早期成岩作用及岩化特征具有重要意义,其形成过程及成因也为古海洋化学条件和底栖生态系统的变化提供了主要依据。