CO2 injection has emerged as a promising technique for enhancing the shale oil recovery. During oil extraction from nanopores, phase separation of the CO2-oil mixture can significantly influence shale oil production. However, current studies on oil extraction always ignore the role of dynamic phase change at the pore scale. In this study, a multicomponent multiphase lattice Boltzmann model was applied to simulate the phase separation of the CO2-oil mixture during extraction. Our simulations reveal three distinct stages of oil extraction from a dead-end nanopore. In the first stage, oil is steadily extracted when the pressure remains above the bubble point. As phase separation begins, liquid flow declines sharply due to the strong capillary resistance. In the third stage, residual oil is either extracted or trapped, depending on pore size and wettability. We further investigated oil extraction from a nanoporous medium. Unlike dead-end pores, improved pore connectivity suppresses the emergence of the three extraction stages. Once phase separation occurs, oil transport in small pores is severely impeded by confinement effects. In contrast, a large fraction of oil is extracted from large pores, contributing over 75% of total recovery. Oil-wet surfaces promote oil extraction from large pores but hinder oil recovery in small pores. Moreover, increasing the CO2 concentrations consistently improves oil extraction in both types of pores.

In this study, we introduce a novel field-based method to estimate specific yield (S-y) in fractured, low-porosity granite aquifers using borehole nuclear magnetic resonance (bNMR). This method requires collecting a bNMR survey immediately following a pump test, which dewaters the near-borehole fractures. The residual water content measured from bNMR is interpreted as "bound" and represents the specific retention (S-r) while the water drained by the pump is the S-y. The transverse relaxation cutoff time (T-2C) is the length of time that partitions the total porosity measured by bNMR into S-r and S-y. When applying a calibrated T-2C, S-y equals the bNMR total porosity minus S-r; thus, a calibrated T-2C is required to determine S-y directly from NMR results. Based on laboratory experiments on sandstone cores, the default T-2C is 33 ms; however, its applicability to fractured granite aquifers is uncertain. The optimal T-2C based on our pumping test is 110 +/- 25 ms. Applying this calibrated T-2C on a saturated, A-type granite at our field site, we estimate the S-y to be 0.012 +/- 0.005 m(3) m(-3) which is significantly different from the S-y (0.021 +/- 0.005 m(3) m(-3)) estimate using the default T-2C of 33 ms. This S-y estimate falls within a range determined using traditional hydraulic testing at the same site. Using the conventional T-2C (33 ms) for fractured granite leads to an inaccurate S-y; therefore, it is essential to calibrate the bNMR T-2C for the local site conditions prior to estimating S-y.

利用薄片鉴定、扫描电镜、阴极发光及碳氧同位素分析等手段,对莺歌海盆地LD10区新近系梅山组—黄流组高温-超压-高CO2背景下的储层成岩作用特征及其对孔隙的影响进行了系统研究.研究结果表明:①莺歌海盆地LD10区新近系梅山组—黄流组储层发育重力流沉积,岩性以中—细粒长石岩屑石英砂岩为主,储层物性以特低—低孔、特低渗特征为主.②压实、胶结和溶蚀作用是研究区主要的成岩作用类型.超压对黏土矿物的转化及石英次生加大具有明显抑制作用,并在一定程度上保护了原生孔隙.富含CO2的高温流体不仅造成了黏土矿物的异常转化,同时促进了溶蚀作用发生,增加了次生孔隙.③研究区黄二段储层的成岩演化序列为:菱铁矿胶结→石英次生加大→绿泥石胶结→长石淋滤溶蚀→高岭石形成→早期方解石胶结→早期白云石胶结→长石溶蚀→方解石溶蚀→伊利石大量生成→晚期铁方解石、铁白云石形成.④总体上,压实作用使孔隙度减少了45.30％～62.93％,胶结作用使孔隙度减少了1.65％～35.01％,溶蚀作用使孔隙度增加了0.72％～8.00％.其中,黄流组中下部砂岩储层受到了超压保护和CO2溶蚀作用的双重影响,物性较好,钻井过程中应考虑高CO2风险.

莺歌海盆地LD10区中深层黄流组-梅山组重力流水道、海底扇储层已被证实具有重大的天然气资源潜力.但是前期测试结果显示气藏中混有高含量CO2气体.因此,精细厘定天然气充注期次,明确CH4、CO2等时空分布规律对规避高CO2风险至关重要.本研究在对不同产状流体包裹体岩相学特征精细观察的基础上,综合激光拉曼光谱分析和包裹体显微测温技术识别出3幕不同成分天然气充注,时间分别为:4.0～2.9 Ma、2.0～1.2 Ma和0.8～0.3 Ma.其中,第一幕充注以烃类气为主,伴有少量有机CO2和N2;第二幕和第三幕充注以大量无机CO2、烃类气为主,伴有少量N2.结合天然气及烃源岩地化特征、天然气组分分析及输导体系识别,总结了LD10区的成藏模式,以期为研究区下一步天然气勘探开发和规避高含量CO2风险提供依据.

We characterized horizontal hydraulic conductivity ( K ) of a fractured granitic aquifer using single‐ and cross‐hole hydraulic tests to evaluate “scale effect.” For selected boreholes, K estimates were obtained using single‐hole FLUTe liner and slug tests. Several cross‐hole pumping tests were carried out at various durations. Drawdown responses were first interpreted using analytical well‐test solutions to obtain an effective horizontal conductivity ( K eff ) assuming a homogeneous and infinite aquifer. The same drawdowns were then numerically inverted using transient hydraulic tomography (THT) to delineate spatial distributions of K and storativity in the area encompassing the boreholes. Papadopulos (1965) and a nonlinear least squares minimization method produced a similar principal K eff direction that is consistent with the dominant fracture strike observed from outcrop and borehole televiewer data. However, principal direction and magnitude of this K eff depend on the pumping test duration and the number of monitoring boreholes used in the interpretation. As a group, K obtained from cross‐hole tests is larger than that obtained from single‐hole tests. However, because cross‐hole tests stressed the aquifer at both interwell and larger scales, K eff obtained from interpreting cross‐hole data is observed to decrease with pumping time, likely due to the dominance of less permeable fractures at larger scale. This lateral reduction of mean K is also revealed by THT as low K zones surrounding the test boreholes. Overall, K is found to increase from single‐hole to the interwell scale and then decrease at larger scale, exhibiting a non‐monotonic scale effect.

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We investigated the hydraulic properties of a fractured granite aquifer in the Laramie Range, Wyoming, using cross-hole pumping tests among six boreholes ranging from 16-76 m deep. Results of four cross-hole pumping tests were interpreted using analytical conceptual models and using SimSLE, a two-dimensional transient hydraulic tomography (HT) algorithm (Xiang et al., 2009). A set of field-scale vertically averaged horizontal hydraulic conductivities (Kh) was interpreted first using analytical models, i.e., Theis (1935), Cooper and Jacob (1946), Neuman (1974), and Moench (1997). The estimated Kh values are very close despite the difference in the assumptions of these analytical models. HT is a useful technique for imaging inter-well permeability heterogeneity. The SimSLE algorithm was able to image, between these boreholes, continuous high Kh and low specific storage (Ss) zones, thus areas with high hydraulic diffusivity. These inter-well zones allow fast preferential flows that reflect connectivity of fractures between the boreholes. In addition, the same algorithm identified a low Kh barrier between one borehole and the rest of the well field, which is consistent with what is known from site geological, drilling, and geophysical data. Finally, scale effect is observed as the pumping-test-inferred Kh is more than a factor of 5 greater than the slug-test-inferred Kh for several boreholes, suggesting fractures with greater permeability were encountered when the well test volume was expanded.

Establishing a high-resolution subsurface model is the ultimate goal of reservoir characterization. The "BQ 10 Block", in Biyang Sag of Nanxiang Basin in China, is a data-rich mature field with heavy oil deposits penetrated by over two hundred wells with an average well spacing of 75m. The aim of this study is to establish a three-dimensional high-resolution model of the BQ 10 reservoir and to accurately and efficiently derive its geological and geometrical properties. A geostatistical modeling study was carried out in combination with stratigraphic correlation, core observations, log interpretation, lithology estimation, and sedimentary facies analysis. Based on core and wireline log data, lithology and conventional well logs (i.e. resistivity, gamma ray, and spontaneous potential) were correlated first. Lithofacies data at cored well locations were grouped into petrofacies units based on reservoir quality data. Using a neural network method, petrofacies at uncored wells was predicted based on correlation with conventional well logs. For different petrofacies, statistical analyses revealed correlation between laboratory porosity and permeability with acoustic well logs. A petrofacies model was built alternatively with indicator kriging, truncated Gaussian simulation (TGS), and sequential indicator simulation (SIS). SIS with a 3D trend model was identified to give the most reasonable petrofacies distribution. Using this model, facies-controlled petrophysical property modeling was performed using sequential Gaussian simulation (SGS). A validation procedure based on "minimum acceptance criteria" was employed to ensure that the SIS/SGS realizations are consistent. For this data-rich reservoir, this study demonstrates an effective application of the standard geostatistical modeling techniques on constructing high-resolution reservoir models of a heavy oil reservoir. The final suite of models reveal a likely range of reservoir facies and petrophysical property distributions for BQ 10, which can be useful for designing heavy oil recovery operations.

In granite aquifers, fractures can provide both storage volume and conduits for groundwater. Characterization of fracture hydraulic conductivity (K) in such aquifers is important for predicting flow rate and calibrating models. Nuclear magnetic resonance (NMR) well logging is a method to quickly obtain near-borehole hydraulic conductivity (i.e., KNMR ) at high-vertical resolution. On the other hand, FLUTe flexible liner technology can produce a K profile at comparable resolution but requires a fluid driving force between borehole and formation. For three boreholes completed in a fractured granite, we jointly interpreted logging NMR data and FLUTe K estimates to calibrate an empirical equation for translating borehole NMR data to K estimates. For over 90% of the depth intervals investigated from these boreholes, the estimated KNMR are within one order of magnitude of KFLUTe . The empirical parameters obtained from calibrating the NMR data suggest that "intermediate diffusion" and/or "slow diffusion" during the NMR relaxation time may occur in the flowing fractures when hydraulic aperture are sufficiently large. For each borehole, "intermediate diffusion" dominates the relaxation time, therefore assuming "fast diffusion" in the interpretation of NMR data from fractured rock may lead to inaccurate KNMR estimates. We also compare calibrations using inexpensive slug tests that suggest reliable KNMR estimates for fractured rock may be achieved using limited calibration against borehole hydraulic measurements.

Fractured crystalline aquifers of mountain watersheds may host a significant portion of the world's freshwater supply. To effectively utilize water resources in these environments, it is important to understand the hydraulic properties, groundwater storage, and flow processes in crystalline aquifers and field-derived insights are critically needed. Based on borehole hydraulic characterization and monitoring data, this study inferred hydraulic properties and groundwater flow of a crystalline fractured aquifer in Laramie Range, Wyoming. At three open holes completed in a fractured granite aquifer, both slug tests and FLUTe liner profiling were performed to obtain estimates of horizontal hydraulic conductivity (K-h). Televiewer (i.e., optical and acoustic) and flowmeter logs were then jointly interpreted to identify the number of flowing fractures and fracture zones. Based on these data, hydraulic apertures were obtained for each borehole. Average groundwater velocity was then computed using K-h, aperture, and water level monitoring data. Finally, based on all available data, including cores, borehole logs, LIDAR topography, and a seismic P-wave velocity model, a three dimensional geological model of the site was built. In this fractured aquifer, (1) borehole K-h, varies over similar to 4 orders of magnitude (10(-8)-10(-5) m/s). K-h is consistently higher near the top of the bedrock that is interpreted as the weathering front. Using a cutoff K-h of 10(-10)m/s, the hydraulically significant zone extends to similar to 40-53 m depth. (2) FLUTe-estimated hydraulic apertures of fractures vary over 1 order of magnitude, and at each borehole, the average hydraulic aperture by FLUTe is very close to that obtained from slug tests. Thus, slug test can be used to provide a reliable estimate of the average fracture hydraulic aperture. (3) Estimated average effective fracture porosity is 4.0 x 10(-4), therefore this fractured aquifer can host significant quantity of water. (4) Natural groundwater velocity is estimated to range from 0.4 to 81.0 m/day, implying rapid pathways of fracture flow. (5) The average ambient water table position follows the boundary between saprolite and fractured bedrock. Groundwater flow at the site appears topography driven.

泌阳凹陷古城油田泌浅10区核三段广泛发育三角洲前缘水下分流河道薄层砂体.在储层精细沉积微相研究的基础上,综合应用岩芯、密井网测井等资料,对古城水下分流河道单砂体进行了精细刻画,建立了单砂体规模定量预测模型.依据河道规模将古城水下分流河道分为Ⅰ型、Ⅱ型、Ⅲ型河道3类.运用高分辨率层序地层学短期基准面旋回原理,对研究层段水下分流河道砂体成因类型进行了研究.结果表明,在基准面低幅上升且A/S＜＜1时,形成削截式水下分流河道砂体;A/S＜1(接近1)时,形成完整式水下分流河道砂体.识别出单一河道砂体的叠置类型主要包括垂向叠置、侧向叠置、垂向相切、侧向相切、垂向分隔5种垂向叠置模式以及间湾相隔式、水平搭接式、侧向切叠式3种平面接触样式,并总结了各自的测井相识别标志.