Evaluation Of The Reservoir-forming Conditions Of The Carboniferous-Permian Shale Gas In The Plain Area Of Hebei Province

In November 2016,the first high-yield industrial gas flow in the marine&terrestrial transitional facies was obtained by fracturing and testing potassium--well 1in lower part of Carboniferous system in Miaozhi,Shaanxi Province,thus achieving major breakthrough of new strata shale gas of Carboniferous in North China.In plain area of Hebei Province,Carboniferous-permian strata is deep buried,thick and widely distributed,at the same time,shale is widely existing,which also has a good prospect of shale gas accumulation of marine&terrestrial transitional facies.At present,geological evaluation of domestic shale gas is divided into three stages:division of prospects?delineating the target layer?,division of favorable areas?delineating the favorable layer?and division of core areas?delineating the core layer?.At the same time,the evaluation standard of favorable areas?favorable layer?is determined.Based on the drilling data in the plain area,the paper evaluates the accumulation conditions of shale gas in Carboniferous-permian strata.By obtaining evaluation parameters,it determines evaluation standard of prospects?target layer?and splits part of standard as the evaluation standard of shale area?shale layer?.Combined with the evaluation methods of stratified deposits,such as coal,the comprehensive evaluation is conducted to stability of shale layer and development degree of the target layer,thus better delineating the target layer,grasping change law,and providing the basis for preference of favorable layer.In order to determine effectiveness of the evaluation method,the prospect in Kaiping is selected as the key working area for verification.Among 9 shale delineated from Benxi formation to Lower Shihezi formation,8 of them have target layers.Three shale layers,including K₁,K₅ and K₇,are relatively stable,and the target layer of K₇is the best.By following up the drilling project,sampling and testing are conducted to three target layers,including K₂,K₃ and K₆.Target layers are analyzed according to test results.It turns out that all of them do not meet the preference standards of favorable layer.The main influencing parameters are:high clay content and low porosity and gas content.The evaluation method is effective through verification.Through the geological evaluation of the whole area,three shale areas in the plain area:Kaiping area,Dacheng area and Handan area are divided according to results of shale delineation.The occurrence scale of shale in Dacheng district is the largest,and the stability of shale in Handan area is the best.The development degree of the target layers in each district is similar.At the same time,10 target layers with parameters do not meet the preference standards of favorable layer.The parameters of gas content are affected by sampling method,so more than 90%of gas is lost in the process of drilling.The isothermal adsorption experiments are carried out to some target layers.By analogy with the relevant data of Qinshui Basin in Shanxi Province,the gas content should be above 1 m³/t,but the porosity of Kaiping area and Handan area is low.The maturity in Dacheng area is low.The clay content in target layers of delta facies is too high in the whole area,which still does not meet the preference standards of favorable layer.There are still 17 target layers that do not obtain preference parameters of the favorable layer,which need to be further studied.