| Zhengzhuang Block is located in the Southern Qinshui Basin.Although the enrichment of coalbed methane(CBM)is high,the gas production and the economic benefits are relatively low for the research limitation of coal development geology and development technology.In order to further recognize coal reservoir geology and reservoir physical property,investigate the controlling factors of CBM well hydraulic fracturing and productivity,this paper comprehensively evaluated CBM development geology in Zhengzhuang Block.Based on the typical features of coal reservoir geology,hydraulic fracturing,water drainage and gas production and productivity,we assessed the fracturing effects and productivity controlling factors,as well as the proper well production process.Five production areas in Zhengzhuang Block were divided into two development units.According to regional geology data and the plane distribution of coal reservoir property,the two units were respectively subdivided into slope zone,uplift zone and fault zone.The distribution of coal reservoir physical characteristics was basically identical with that all over the study area.Four types fracturing curves,including ascending,descending,wavy,and stable types were summarized by analyzing hydraulic fracturing curves.The curve distribution was affected by coal seam structural situation,depth,thickness,cleat and fracture systems and in-situ stress.The fracturing effect was investigated from fracture extension characteristic and gas well productivity.On one hand,coal petrology characteristics,rock-mechanics property,stress condition and the pre-fractures were the main controlling factors of hydraulic fracture extension.On the other hand,based on the study of gas peak,hydraulic fracture conductivity and daily gas production,descending fracturing curve reflected the best fracturing effect,following by stable type curve,and wavy and ascending curve the worst.In this research,typical parameters such as gas breakthrough time,effective production(gas and water),and well bottom flowing pressure were reasonably defined and extracted from plenty of production data.What's more,the corresponding relationship between typical parameters and regional geology was well analyzed.Results showed that there were four types production curves,including stable type,ascending type,decreasing type and wavy type.The stable type production curves always behaved a high gas production,they generally distributed in uplift zone and the uplift region of fault zone,while wells with wavy production curves mainly concentrated in the slope zone and their gas production was very low.Moreover,well production was influenced by CBM enrichment,structural situation,fracturing effect,hydrological characteristics,and water drainage technique.Wells with continuous and high gas production usually had following features:uplift zone with medium intensity tectonic deformation,CBM content was more than 18m~3/t,decreasing type fracturing type,ground water retention area with salinity between 2200mg/L to 2500mg/L,wells with continuous and stable production system.In order to obtain effective fracturing results,it's better to use active water fracturing fluid,and the fluid volume should be controlled between 700m~3 to 750m~3.What's more,variable displacement and multi-stage propped technique helped to improve the fracturing effect.The proper descending speed of producing fluid level was 5~10m/d(about 7.5m/d)during the initial production stage. |
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