Oil and gas exploration in lacustrine mud shale has focused on laminated calcareous lithofacies rich in type Ⅰ or type Ⅱ1 organic matter, taking into account the mineralogy and bedding structure, and type and abunda...Oil and gas exploration in lacustrine mud shale has focused on laminated calcareous lithofacies rich in type Ⅰ or type Ⅱ1 organic matter, taking into account the mineralogy and bedding structure, and type and abundance of organic matter. Using the lower third member of the Shahejie Formation, Zhanhua Sag, Jiyang Depression as the target lithology, we applied core description, thin section observations, electron microscopy imaging, nuclear magnetic resonance, and fullbore formation microimager （FMI） to study the mud shale lithofacies and features. First, the lithofacies were classified by considering the bedding structure, lithology, and organic matter and then a lithofacies classification scheme of lacustrine mud shale was proposed. Second, we used optimal filtering of logging data to distinguish the lithologies. Because the fractals of logging data are good indicators of the bedding structure, gamma-ray radiation was used to optimize the structural identification. Total organic carbon content （TOC） and pyrolyzed hydrocarbons （S2） were calculated from the logging data, and the hydrogen index （HI） was obtained to identify the organic matter type of the different strata （HI vs Tmax）. Finally, a method for shale lithofacies identification based on logging data is proposed for exploring mud shale reservoirs and sweet spots from continuous wellbore profiles.展开更多
Compared with conventional gas reservoirs,shale gas reservoirs are not sensitive to petrophysical properties,making it much difficult to identify this kind of reservoirs with well logging technologies.Therefore,throug...Compared with conventional gas reservoirs,shale gas reservoirs are not sensitive to petrophysical properties,making it much difficult to identify this kind of reservoirs with well logging technologies.Therefore,through a comparison of the logging curves of the Lower Silurian Longmaxi marine shale in the Jiaoshiba area,Sichuan Basin,it is found that the mud shale on conventional log curves generally features high gamma ray,high uranium,low thorium,low kalium,relative high resistivity,high interval transit time,low neutron,low density and low photoelectric absorption cross section index,while on elements logging curves,it features an increase of silicon content and a decrease of aluminum and iron content.Based on the logging response characteristics of mud shale,the logging curves most sensitive to shale,gamma ray,neutron and density logging were selected and overlaid to identify mud shale effectively.On the basis of qualitative identification,the density logging value can identify the non-organic-rich mud shale from organic-rich mud shale,because the former has a density of 2.61–2.70 g/cm^(3),while the latter has a density of less than 2.61 g/cm^(3).The identification results agree well with the results of field gas content test,TOC experiment,and gas logging,so this study can provide reference for the logging interpretation.展开更多
It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model w...It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model was used to characterize the hydration strainrelated strength damage.Considering drilling fluid sealing barrier on shale,a calculation method of safe drilling mud density has been established for shale formation under drilling fluid sealing-inhibition-reverse osmosis effect,combined with a flow-diffusion coupling model.The influence of drilling fluid sealing and inhibiting parameters on safe drilling mud density window was analyzed.The study shows that enhancing drilling fluid sealing performance can reduce the pore pressure transmission and solute diffusion;the inhibiting performance of drilling fluid,especially inhibition to strength damage,is crucial for the wellbore collapse pressure of shale section with significant hydration property.The improvement of drilling fluid sealing and inhibition performance can lower collapse pressure and enhance fracturing pressure,and thus making the safe drilling fluid density window wider and the collapse period of wellbore longer.If there is osmosis flow in shale,induced osmosis flow can make the gap between collapse pressure and fracturing pressure wider,and the stronger the sealing ability of drilling fluid,the wider the gap will be.The safe drilling mud density window calculation method can analyze the relationships between collapse pressure,fracturing pressure and drilling fluid anti collapse performance,and can be used to optimize drilling fluid performance.展开更多
基金This work was supported by the National Natural Science Foundation of China （Nos. 41202110 and 51674211） and Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation （Southwest Petroleum University） （No. PLN201612）, the Applied Basic Research Projects in Sichuan Province （No. 2015JY0200） and the Open Fund Project from Sichuan Key Laboratory of Natural Gas Geology （No. 2015trqdz07）.
文摘Oil and gas exploration in lacustrine mud shale has focused on laminated calcareous lithofacies rich in type Ⅰ or type Ⅱ1 organic matter, taking into account the mineralogy and bedding structure, and type and abundance of organic matter. Using the lower third member of the Shahejie Formation, Zhanhua Sag, Jiyang Depression as the target lithology, we applied core description, thin section observations, electron microscopy imaging, nuclear magnetic resonance, and fullbore formation microimager （FMI） to study the mud shale lithofacies and features. First, the lithofacies were classified by considering the bedding structure, lithology, and organic matter and then a lithofacies classification scheme of lacustrine mud shale was proposed. Second, we used optimal filtering of logging data to distinguish the lithologies. Because the fractals of logging data are good indicators of the bedding structure, gamma-ray radiation was used to optimize the structural identification. Total organic carbon content （TOC） and pyrolyzed hydrocarbons （S2） were calculated from the logging data, and the hydrogen index （HI） was obtained to identify the organic matter type of the different strata （HI vs Tmax）. Finally, a method for shale lithofacies identification based on logging data is proposed for exploring mud shale reservoirs and sweet spots from continuous wellbore profiles.
基金National Science and Technology Major Project“Appraisal of shale gas resources and selection of play in Shangyangzi and Yunnan-Guizhou areas”(No.14B12XQ151001).
文摘Compared with conventional gas reservoirs,shale gas reservoirs are not sensitive to petrophysical properties,making it much difficult to identify this kind of reservoirs with well logging technologies.Therefore,through a comparison of the logging curves of the Lower Silurian Longmaxi marine shale in the Jiaoshiba area,Sichuan Basin,it is found that the mud shale on conventional log curves generally features high gamma ray,high uranium,low thorium,low kalium,relative high resistivity,high interval transit time,low neutron,low density and low photoelectric absorption cross section index,while on elements logging curves,it features an increase of silicon content and a decrease of aluminum and iron content.Based on the logging response characteristics of mud shale,the logging curves most sensitive to shale,gamma ray,neutron and density logging were selected and overlaid to identify mud shale effectively.On the basis of qualitative identification,the density logging value can identify the non-organic-rich mud shale from organic-rich mud shale,because the former has a density of 2.61–2.70 g/cm^(3),while the latter has a density of less than 2.61 g/cm^(3).The identification results agree well with the results of field gas content test,TOC experiment,and gas logging,so this study can provide reference for the logging interpretation.
基金Supported by the China National Science and Technology Major Project(2016ZX05020-003).
文摘It is difficult to define safe drilling mud density window for shale sections.To solve this problem,the general Biot effective stress principle developed by Heidug and Wong was modified.The Weibull statistical model was used to characterize the hydration strainrelated strength damage.Considering drilling fluid sealing barrier on shale,a calculation method of safe drilling mud density has been established for shale formation under drilling fluid sealing-inhibition-reverse osmosis effect,combined with a flow-diffusion coupling model.The influence of drilling fluid sealing and inhibiting parameters on safe drilling mud density window was analyzed.The study shows that enhancing drilling fluid sealing performance can reduce the pore pressure transmission and solute diffusion;the inhibiting performance of drilling fluid,especially inhibition to strength damage,is crucial for the wellbore collapse pressure of shale section with significant hydration property.The improvement of drilling fluid sealing and inhibition performance can lower collapse pressure and enhance fracturing pressure,and thus making the safe drilling fluid density window wider and the collapse period of wellbore longer.If there is osmosis flow in shale,induced osmosis flow can make the gap between collapse pressure and fracturing pressure wider,and the stronger the sealing ability of drilling fluid,the wider the gap will be.The safe drilling mud density window calculation method can analyze the relationships between collapse pressure,fracturing pressure and drilling fluid anti collapse performance,and can be used to optimize drilling fluid performance.
