Xu, Wei (CNOOC Research Institute Co., Ltd.) | Chen, Kaiyuan (Beijing Key Laboratory of Unconventional Natural Gas Geological Evalution and Development Engineeing, China University of Geosciences Beijing) | Fang, Lei (Beijing Key Laboratory of Unconventional Natural Gas Geological Evalution and Development Engineeing, China University of Geosciences Beijing) | Zhang, Yingchun (CNOOC Research Institute Co., Ltd.) | Jing, Zhiyi (CNOOC Research Institute Co., Ltd.) | Liu, Jun (CNOOC Research Institute Co., Ltd.) | Zou, Jingyun (CNOOC Research Institute Co., Ltd.)
The lacustrine delta sandbody deposited in the north of Albert Basin is unconsolidated due to the shallow burial depth, which leads to an ultra-high permeability (up to 20 D) with large variation and poor diagenesis. Log derived permeability differs greatly with DST results. Thus, permeability simulation is challenging in 3D geomodeling. A hierarchical geomodeling approach is presented to bridge the gap among the ultra-high permeability log, model and DST results. The ultimate permeability model successfully matched the logging data and DST results into the geological model.
Based on the study of sedimentary microfacies, the new method identifies different discrete rocktypes (DRT) according to the analyis of core, thin section and conventional and special core analysis (e.g., capillary pressure). In this procedure, pore throat radius, flow zone index (FZI) and other parameters are taken into account to identify the DRT. Then, hierarchical modeling approach is utilized in the geomodeling. Firstly, the sedimentary microfacies model is established within the stratigraphic framework. Secondly, the spatial distribution model of DRT is established under the control of sedimentary microfacies. Thirdly, the permeability distribution is simulated according to the different pore-permeability relation functions derived from each DRT. Finally, the permeability model is compared with the logging and testing results.
Winland equation was improved based on the capillary pressure (Pc) data of special core analysis. It is found that the highest correlation between pore throat radius and reservoir properties was reached when mercury injection was 35%. The corresponding formula of R35 is selected to calculate the radius of reservoir pore throat. Reservoirs are divided into four discrete rock types according to parameters such as pore throat radius and flow zone index. Each rock type has its respective lithology, thin section feature and pore-permeability relationship. The ultra-high permeability obtained by DST test reaches up to 20 D, which belongs to the first class (DRT1) quality reservoir. It is located in the center of the delta channel with high degree of sorting and roundness. DRT4 is mainly located in the bank of the channels. It has a much higher shale content and the permeability is generally less than 50 mD. Through three-dimensional geological model, sedimentary facies, rock types and pore-permeability model are coupled hierarchically. Different pore-permeability relationships are given to different DRTs. After reconstructing the permeability model, the simulation results are highly matched with the log and DST test results.
This hierarchical geomodeling approach can effectively solve the simulation problem in the ultra-high permeability reservoir. It realizes a quantitative characterization for the complex reservoir heterogeneity. The method presented can be applied to clastic reservoir. It also plays a significant positive role in carbonate reservoir characterization.
Lu, Chuan (Department of Civil and Environmental Engineering, University of Alberta) | Brandl, Jakob (Department of Civil and Environmental Engineering, University of Alberta) | Deisman, Nathan (Department of Civil and Environmental Engineering, University of Alberta) | Chalaturnyk, Richard (Department of Civil and Environmental Engineering, University of Alberta)
In this study, a novel experimental system has been developed for static and dynamic elastic properties measurements at seismic frequencies under anisotropic stress and shear deformation conditions. This system focuses on static and seismic range frequencies dynamic (0.1 Hz to 20 Hz) elastic deformation properties of poorly consolidated oil sands and highly overconsolidated (clay) shales. The main body of the experimental system is a computer control servo-hydraulic system. A pair of laser displacement sensors measure nanometer scale displacement during the dynamic tests. A coarse scale and fine scale load cell system was developed for measuring force with high precision during dynamic testing. A novel triaxial cell for use with the loading system was also developed to simulate the reservoir stress and pore pressure condition during static and dynamic testing and allows permeability to be measured during testing. The loading system, dual load cell calibration procedure and results, and results for acrylic and 3D printed sand specimens are presented. The stable and reasonable results demonstrate the capacity of the new experimental system.
A new cased-hole porosity measurement has been developed for a four-detector pulsed-neutron logging tool. The measurement is based on a capture count rate ratio from two different detectors. To determine an accurate porosity, the ratio is characterized in the laboratory in order to establish a ratio-to-porosity transform. To account for varying measurement conditions in the field, environmental corrections, based on laboratory studies and computer simulation, are applied. As an alternative to environmental corrections, the capture ratio can also be actively compensated for the environment by using the results of a dual-exponential fit to the capture time decay spectrum. In particular, we can compensate for the borehole fluid salinity by using the borehole component of the dual-exponential fit, and we can compensate for the effective density of the borehole environment by using an inelastic ratio derived from the capture subtracted burst yields. The final porosity measurement has been shown to provide accurate results in the field through a comparison with data from open-hole logs.
Almeida da Costa, Alana (Universidade Federal da Bahia) | Jaeger, Philip (Eurotechnica GmbH) | Santos, Joao (Láctea Científica) | Soares, João (University of Alberta) | Trivedi, Japan (University of Alberta) | Embiruçu, Marcelo (Universidade Federal da Bahia) | Meyberg, Gloria (Universidade Federal da Bahia)
Low salinity waterflooding and CO2 injection are enhanced oil recovery (EOR) methods that are currently growing at a substantial rate worldwide. Linking these two EOR methods appears to be a promising approach in mature fields and for the exploration of post- and pre-salt basins in Brazil. Moreover, the latter reservoirs already have high CO2 content in the gas phase. Interfacial phenomena between fluids and rock in low salinity brine/CO2 environment still remain unclear, particularly the wettability behavior induced by the pH of the medium. In this study, coreflooding experiments, zeta potential, contact angle, interfacial tension (IFT), and pH measurements at ambient and reservoir conditions were performed to investigate the influence of the rock composition and brine/CO2 mixtures at different pH values for low salinity water-CO2 EOR (LSW-CO2 EOR) applications in Brazilian reservoirs. Brazilian light crude oil, pure CO2, and different brine solutions were used to represent the fluids in actual oil reservoirs. The experiments were carried out on Botucatu sandstone samples, with mineralogy determined by energy dispersive X-ray analysis. Coreflooding experiments were conducted by injection of 10 pore volumes of high salinity water followed by low salinity water. Contact angles, IFT and pH measurements at atmospheric and elevated pressures were performed in a high-pressure view cell (
Nguyen, Nhat (The University of Texas at Austin) | Ren, Guangwei (TOTAL E&P R&T, USA) | Mateen, Khalid (TOTAL E&P R&T, USA) | Ma, Kun (TOTAL E&P R&T, USA) | Luo, Haishan (TOTAL E&P R&T, USA) | Neillo, Valerie (TOTAL SA) | Nguyen, Quoc (The University of Texas at Austin)
Low-Tension Gas (LTG) has emerged as a novel enhanced oil recovery injection strategy, employing foam in place of polymer to displace the oil bank created with the help of ultra-low-IFT (ULIFT). In our prior work, the process was successfully employed, both in sandstones and carbonates, to achieve attractive oil recoveries with relatively low surfactant retention. However, earlier experiments were carried out at high flow rates in relatively high permeability cores. To improve the robustness of this novel injection scheme, it is necessary to examine it under wider practical environments. Therefore, in this work, experiments are conducted in carbonate and sandstone cores, at lower injection rates and rock permeabilities, to determine whether the foam could provide the necessary mobility control with this novel EOR technique. Initially, a lower flow rate (1 ft/D) experiment is conducted in relatively high permeability (388 md) sandstone core to compare it with the earlier results under a higher injection rate (4 ft/D). Subsequently, even further reduced injection rate (0.5 ft/D) is employed in a sandstone core with one order of magnitude lower permeability (36 md). Two other corefloods with Estaillades limestone (166 md) and Richmont (7 md) are carried out to extend the comparison to carbonate rocks. Surfactant retentions are determined. It is found that four-times-lower injection rate (1ft/D) just slightly delayed oil production, and achieved comparably high oil recovery (87%), indicating a good mobility control. Proportionally reduced pressure drop during slug injection implies similar total fluid mobility. Accordingly, salinity propagation examined from effluents shows slight delays. Even with ten-times-lower permeability sandstone (36 md) at a lower total injection rate (0.5 ft/D), comparable oil recovery (84%) and salinity propagation are found, despite of much lower foam strength. With an intermediate-permeability Estaillades limestone (166 md), compared to high permeability sandstone, oil production is delayed, but comparable eventual oil recovery (88%) is obtained. The delay could be due to higher surfactant retention (0.301 mg/g). The delayed effluent salinity propagation is noticeable, which may be caused by increased total fluid mobility. Finally, extremely low permeability Richmont (7 md) indeed adversely impacts the oil recovery (~58%) and the salinity propagation. This could be attributed to higher surfactant retention and/or decreased foam stability due to oil-wet rock surface. The works here test the robustness of the LTG process in more practical reservoir conditions and have widened its applicability. Demonstration of its feasibility in low-permeability reservoirs, where use of polymer is not currently feasible, will greatly promote the testing and deployment of this technology in the future.
Rock compressibility has great influence in the original oil in place estimation, history matching, and production forecasting. The majority of the reservoir engineers consider the compressibility as a constant throughout the life of a field, but it is well known that rock compressibility is pressure and porosity dependent. During the life of an oil field, the pore pressure decreases with oil production, which increases the net pressure over the reservoir which induces changes in porosity and in compressibility. Neglect compressibility variation may induce several errors during reservoir simulation. To reduce errors, and to provide a simple and easy procedure for calculation of rock compressibility, this paper presents the correlation between rock compressibility and porosity under hydrostatic confining test, as well as the corrections made to translate unrealistic hydrostatic data into more representative uniaxial data. The measurements were developed in 5 sandstones and 5 carbonate rocks with a diversified range in porosity and rock strength to obtain results more capable to describe any other set of data. The results of the corrections were then plotted against porosity and a new general equation was derived from the plots through data fitting. The new equation proved to be very representative, but it faced an issue related to the inverse problem. To fix the problem, the Poisson ration was applied to the general equations to capture the mechanical characteristics of the rocks. The results showed that rock compressibility has a direct relation to porosity. Further, the conversion factors displayed high efficiency in the translation from hydrostatic data to uniaxial data, and hydrostatic compressibility may increase the errors during estimation of the volume of original oil in place by a factor of 1E+6 STB. Also, the error in the volume of OOIP calculated using
Many investigations have been discussed and it is a well-recognized fact that sonic wave velocity is not only influenced by its rock matrix and the fluids occupying the pores but also by the pore architecture details of the rock bulk. This situation still brings a lack of understanding, and this study is purposed to clearly explain how acoustic velocity and quality factor correlate with porosity, permeability and details internal pore structure in porous rocks.
This study employs 67 sandstone and 120 carbonate core samples collected from several countries in Europe, Australia, Asia, and USA. The measured values are available for porosity
At least eight rock groups are established from rock typing with its Kozeny constant. This constant is a product of pore shape factor
As a novelty, the empirical equations are derived to estimate compressional velocity and quality factor based on petrophysical parameters. Furthermore, this study also establishes empirical equations for predicting porosity and permeability by using compressional wave velocity, critical porosity, and PGS rock typing.
Lin, Qingyang (Imperial College London) | Alhammadi, Amer M. (Imperial College London) | Gao, Ying (Imperial College London) | Bijeljic, Branko (Imperial College London) | Blunt, Martin J. (Imperial College London)
We combine steady-state measurements of relative permeability with pore-scale imaging to estimate local capillary pressure. High-resolution three-dimensional X-ray tomography enables the pore structure and fluid distribution to be quantified at reservoir temperatures and pressures with a resolution of a few microns. Two phases are injected through small cylindrical samples at a series of fractional flows until the pressure differential across the core is constant. Then high-quality images are acquired from which saturation is calculated, using differential imaging to quantify the phase distributions in micro-porosity which cannot be explicitly resolved. The relative permeability is obtained from the pressure drop and fractional flow, as in conventional measurements. The curvature of the fluid/fluid interfaces in the larger pore spaces is found, then from the Young-Laplace equation, the capillary pressure is calculated. In addition, the sequence of images of fluid distribution captures the displacement process. Observed gradients in capillary pressure – the capillary end effect – can be accounted for analytically in the calculation of relative permeability.
We illustrate our approach with three examples of increasing complexity. First, we compare the measured relative permeability and capillary pressure for Bentheimer sandstone, both for a clean sample and a mixed-wet core that had been aged in reservoir crude oil after centrifugation. We characterize the distribution of contact angles to demonstrate that the mixed-wet sample has a wide range of angle centred, approximately, on 90°. We then study a water-wet micro-porous carbonate to illustrate the impact of sub-resolution porosity on the flow behaviour: here oil, as the non-wetting phase, is present in both the macro-pores and micro-porosity. Finally, we present results for a mixed-wet reservoir carbonate. We show that the oil/water interfaces in the mixed-wet samples are saddle-shaped with two opposite, but almost equal, curvatures in orthogonal directions. The mean curvature, which determines the capillary pressure, is low, but the shape of the interfaces ensures, topologically, well-connected phases, which helps to explain the favourable oil recovery obtained in these cases.
We suggest that the combination of imaging and flow experiments – which we call iSCAL – represents a compelling development in special core analysis. This methodology provides the data traditionally acquired in SCAL studies, but with insight into displacement processes, rigorous quality control, and flexibility over sample selection, while generating detailed datasets for the calibration and validation of numerical pore-scale flow models.
Wei, Bing (Southwest Petroleum University) | Zhang, Xiang (Southwest Petroleum University) | Gao, Ke (Southwest Petroleum University) | Li, Yibo (Southwest Petroleum University) | Pu, Wanfen (Southwest Petroleum University)
CO2 injection, either miscible or immiscible, has been recognized as a promising method to enhance oil production for tight reservoirs, with major projects in progress worldwide. This work targeted a tight sandstone reservoir in China, located in the Lucaogou formation of Jimsar sag, Junggar Basin. CO2 injection using huff-puff method was planned to stimulate the oil production because of the rapidly declining productivity of the existing horizontal wells. Although some laboratory works have been conducted for this site, there still lacks the knowledge of mobilizing process of the matrix oil when natural fractures are present. Herein, we present an experimental study of CO2 huff-n-puff in a fractured sandstone rock with the primary objective of elucidating the oil recovery dynamics in different phases under reservoir conditions. The results indicated that the oil recovery rate rapidly decreased with cycle numbers and CO2 huff-n-puff primarily recovered the oil in the large matrix pores. After three cycles, an incremential 32.2% of the original oil-in-place (OOIP) was produced. Based on the dynamics of oil mobilization, the main-determining-forces (MDFs) in this process were re-defined. CO2 displacement, CO2-oil interaction driven by diffusion, and depressurization dominated the first cycle, whereas from the second cycle the first two forces became insignificant. This implied that the soaking phase could be minimized or even eliminated from the second cycle in order to reduce the shut-in time in field application.
Reservoir characterisation for modelling and flow simulation is done assuming the homogenous nature of the rock. Heterogeneity is overlooked to prevent occurrences of reserve management complexities. Bioturbated sandstone reservoirs are heterogeneous and prominently found in many petroleum producing basins. Studying the fluid characteristics of these heterogeneous systems is essential, as with changing characters will affect the resulting wettability behaviour. Thus, in a bioturbated heterogeneous reservoir, estimation of the wettability will help in estimating the flow behaviour and possible outcomes of hydrocarbon oil and gas recovery from such formations. With this background, a collective approach has been designed to understand the reservoir behaviour of bioturbated sandstones from Kachchh Basin. The samples are from outcrop, and the analysis includes established standard experimental procedures of core/rock analysis for estimating wettability. The paper explores the experimental analysis of the measuring contract angle in various bioturbated samples. Contact angles of both oil-wet and water-wet cores were measured considering time and gradient factors. Capillary pressure of the various grades of bioturbated sandstones was calculated combining obtained data on contact angle values along with the pore size (radius) and interfacial tension data. The results suggest that the final model can be designed and proposed for the characterisation of bioturbated heterogeneous sandstones using the Capillary pressure behaviour of rocks along with hysteresis trend of imbibition and drainage flows.