A New Approach To Calculate Gas Saturation in Shale Reservoirs

Abstract

In recent years, China's shale gas exploration and development has achieved immense development, but the evaluation of fluid saturation in shale gas reservoirs is still not well documented. The Mesozoic Chang 7 Formation is one of the main source rocks in the Ordos Basin and has also proven to have good shale gas accumulation conditions. At present, there are a few methods to directly obtain gas saturation in shale reservoirs, and the conventional method using Archie's equation (which is mainly designed for pure sandstone reservoirs) is still accepted by most researchers. However, because shales usually contain some amount of clay minerals, the accuracy of the calculated gas saturation is reduced. To compensate for the presence of clay minerals, the Waxman-Smits (W-S) model was proposed, with high applicability in the quantitative calculation of water saturation. In this study, we calculated the oil saturation values of the Chang 7 Formation and compared the results with laboratory-measured values. Furthermore, we complimented our results with the support vector machine (SVM) machine-learning algorithm to make up for sparse data from the laboratory measurements. Our results suggest that gas saturation in shale reservoirs can be obtained by the calculation of oil saturation first, using laboratory-measured litho-electric and pyrolysis data, as well as using the W-S model. When the results were applied to other locations in the study area, the results were consistent with the calculated gas saturation values using previously proposed (laborious) methodologies. This suggests that the methods described here can be applied to calculate gas saturation in unconventional reservoirs.

Perspectives of Machine Learning Development on Kerogen Molecular Model Reconstruction and Shale Oil/Gas Exploitation

“…Also, the completion and stimulation parameters of nearly 2700 wells are used to predict the Marcellus shale’s initial production and optimize the oil wells . The SVM algorithm is proposed to evaluate the oil/gas saturation of the Ordos shale reservoir …”

“…155 The SVM algorithm is proposed to evaluate the oil/gas saturation of the Ordos shale reservoir. 156 Various components are contained in the shale, and the heterogeneous distribution of each component in the shale will affect its mechanical parameters, permeability, etc. Therefore, it is challenging to establish a simple mathematical model to describe the heterogeneous shale.…”

Current Status and Prospects of Artificial Intelligence Technology Application in Oil and Gas Field Development

“…The development of artificial intelligence has gone through multiple stages, facing many difficulties, as well as opportunities and development. Through the intelligent application of multiple links such as dynamic analysis of oil and gas reservoirs, intelligent historical fitting, numerical simulation models, and optimization of production plans, the state of oil and gas can be described more accurately . The goal is to develop more scientific development plans to improve the speed and recovery rate of oil and gas extraction .…”

Research on the Shale Reservoir Sensitivity by Using the Mineral Analysis Method

“…Damage to oil and gas reservoirs is essentially a decrease in permeability caused by changes in the pore structure of the rock. − Diagnosis and determination of damage mechanisms need to be based on core analysis, sensitivity assessment, working fluid damage simulation experiments, and field evaluation. − Specific aspects, types, and processes of damage occurrence are revealed through comprehensive analysis. − A large number of scholars believe that the intrusion of working fluid filtrate is the main damage factor in low permeability tight gas reservoirs. − The permeability of the core matrix in such gas reservoirs is very low, and the median radius of the throat is less than 1 μm, showing high capillary force characteristics. − The initial water saturation of the reservoir is often lower than the bound water saturation, leading to easy retention of the working fluid filtrate intruding into the core and difficult to flow back, which can easily lead to a significant reduction in the gas permeability and the formation of serious water-phase trap damage. − When drilling in the reservoir section, the reservoir damage originates from drilling fluid leakage or filtration under the effect of positive differential pressure in the wellbore and capillary forces. − Intrusion into the solid phase can cause reservoir fractures and pore throat plugging, while intrusion into the liquid phase is prone to sensitivity damage and water-phase trap damage. − The depth of drilling fluid intrusion and the degree of damage increase with the increase of positive differential pressure in the wellbore and drilling time. − Among them, as an important development direction of oil and gas wells, it is crucial to study the damage factors and extent of horizontal wells. − Horizontal wells are an important means to increase the production capacity of oil and gas wells, but in many cases, the actual production capacity of horizontal wells cannot meet the expected plan. − The main fluid-sensitive minerals in shale are clay minerals. − The high content and diverse...…”