Hu, Zhenhua (PetroChina Liaohe Oilfield Company) | Zhang, Shenqin (PetroChina Qinghai Oilfield Company) | Wu, Fangfang (Schlumberger) | Liu, Xunqi (Schlumberger) | Wu, Jinlong (Schlumberger) | Li, Shenzhuan (Schlumberger) | Wang, Yuxi (Schlumberger) | Zhao, Xianran (Schlumberger) | Zhao, Haipeng (Schlumberger)
The igneous reservoir of Shahejie formation in eastern sag of Liaohe depression is characterized by complex geological environment, variable lithology and high heterogeneity. Reservoir evaluation is difficult only based on conventional logs due to complex lithology and pore structures. Effective igneous reservoirs were identified and reservoir controlling factors were analyzed based on effective porosity calculation, pore structure analysis, lithology identification, lithofacies analysis, fracture evaluation and heterogeneity analysis by combing nuclear magnetic resonance data, micro-resistivity image data, conventional logs as well as mud logging data.
Based on our study, the igneous reservoirs in the study area are more related with effective porosity and pore connectivity, and less related with fractures. Good reservoirs are mainly distributed on the top part of explosive facies and effusive facies, where lithologies are mainly Trachyte, volcanic breccia and breccia-bearing tuff. The weathering leaching process is quite important for igneous reservoirs, but the reservoir qulity would not be good if the weathering process is too strong as it will lead to low effective porosity.
The accuracy of igneous reservoir evaluation gets improved a lot by this integrated approach and the conclusion from this study will help to optimize igneous reservoire exploration plan.
Hou, Yu Ting (Petrochina ChangQing Oilfield Company) | Xi, Sheng Li (Petrochina ChangQing Oilfield Company) | Wu, Yong (Petrochina ChangQing Oilfield Company) | Li, Huayang (Schlumberger) | Zhao, Xianran (Schlumberger) | Wu, Jinlong (Schlumberger) | Zhao, Haipeng (Schlumberger)
Unconventional reservoirs oil and gas resources have great potential for development, especially in North America, which has been successfully achieved commercial production. Shale oil is one of the unconventional resources. Most of the shale oil reservoirs have complex lithology, poor petrophysical characteristics, complex pore structure, and so on, especially for lacustrine shale oil formation. This paper describes an approach and workflow to characterize the Chang7-3 member shale oil reservoir in the Ordos basin, China by integrating the high tech digital rock physics core analysis data with other special core analysis data to calibrate the reservoir petrophysical properties. The special unconventional core analysis method taken for this project are Tight Reservoir Analysis technology (TRA), Thin Section scanning (TS scanning), Mercury Injection Capillary Pressure test (MICP), N2 and CO2 Gas sorption test, XRD and Nuclear Magnetic Resonance analysis (NMR), and the new logging technology employed are gamma ray spectroscopy logging (LithoScanner*), nuclear magnetic resonance logging (CMR*), dielectric logging (ADT*). The new core analysis and logging technology not only depict the characters of the shale oil reservoir from microscopic to macroscopic scale, but also guarantee to establish the accurate method for reservoir identification and evaluation. The data analysis from above led to the development of evaluation models for organic matter quality and reservoir quality. Analysis of the production data revealed that the hydrocarbon abundance of the Chang7-3 member lacustrine shale oil reservoir is controlled by both organic matter quality and reservoir quality. A production forecast chart of Chang7-3 Member lacustrine shale oil reservoir was constructed based on the organic matter quality and reservoir quality. The application of the developed methodology and workflow achieved very good results and is supported by the test data from multiple wells drilled in the study area.
The lithology of a producing gas reservoir in an area of the Sichuan basin in southwest China is a complex carbonate. Core analysis has revealed a strong correlation between dolomitization and reservoir quality, the process of dolomitization increases reservoir porosity and permeability, and hence overall reservoir rock quality. As such dolomite content is a key parameter in the classification of reservoir rock quality.
Historically, in carbonate reservoirs the estimation of dolomite content from wellbore geophysical data has been via neutron-density cross-plots. The technique was successful when reservoir lithology was relatively simple, such as a combination of limestone and dolomite, and the reservoir fluid was either oil or water. The presence of gas can shift both the neutron porosity and formation density measurements such that a dolomite lithology could be misinterpreted as limestone. However, the photo-electric absorption measurement acquired with modern formation density logs is strongly dependent on lithology and only minimally affected by reservoir fluid. Hence from the combination of neutron porosity, formation density and photo-electric absorption one can resolve simple carbonate lithology even in the presence of gas.
The aforementioned gas reservoir in the Sichuan basin has both high reservoir pressures and high concentrations of H2S, hence to maintain a safe drilling environment the drilling fluid is weighted with barite. The addition of barite makes photo-electric absorption measurements meaningless for petrophysical evaluation.
This paper describes a new technique to accurately describe complex reservoir lithology from elemental capture spectroscopy. The technique is independent of photo-electric absorption and includes elemental measurements of magnesium, calcite, quartz and sulfur. Additionally formation matrix density is derived from the measured elements, which dramatically improves the evaluation of formation porosity. A field example is shown where excellent agreement with core is achieved.