页岩气水平井产量影响因素分析

Key factors influencing shale gas horizontal well production

中国是全球第3个商业化开发页岩气的国家,到2030年页岩气规划产量为800×10~8~1 000×10~8 m^3,展现出良好的发展前景。长宁—威远和昭通国家级页岩气示范区页岩气开发效果显示,目前该区页岩气水平井平均测试产量达到19×10~4 m^3/d,但测试产量却高低参差不齐。为此,从地质和工程两个方面分析了上述示范区页岩气水平井产量影响因素,提出了不同区块水平井提高单井产量的技术方向;根据含气量差异将优质页岩段进一步细分为4类储层,评价水平井Ⅰ类储层钻遇率;依据天然裂缝发育程度、主应力非均质性、脆性指数等工程参数来评价储层改造条件;建立压裂加液量、加砂量、施工排量和返排率与测试产量之间的相关关系;评价压裂形成裂缝复杂程度。研究结果表明:①长宁区块Ⅰ类储层钻遇率高于威远和昭通区块,且当水平井Ⅰ类储层钻遇率大于50%,可保障气井测试页岩气产量高于15×10~4 m^3/d、预计单井最终可采储量(EUR)高于8 000×10~4 m^3;②昭通区块储层改造条件和压裂形成的裂缝复杂程度均优于长宁和威远区块,但加砂量和施工排量等压裂施工参数偏低,制约了前者水平井的测试产量。结论认为,昭通和威远区块进一步提高Ⅰ类储层钻遇率、昭通区块进一步优化压裂施工参数是提高上述示范区页岩气水平井单井产量的主要技术方向。

China is now the third country in the world to have commercially developed shale gas as one of the important unconventional natural gas resources and has built three national demonstration blocks in the Sichuan Basin. Shale gas production is scheduled to reach 80 to 100 billion cubic meters in 2030 by the National Energy Administration of China, showing good prospects. Pilot development in the Changning-Weiyuan and Zhaotong demonstration blocks shows that an average test production of 19× 10^4 m3/d was achieved by those horizontal shale gas wells but the test production rates of different wells show a great variety . In view of this, key factors influencing horizontal shale gas well production were analyzed in terms of geology and engineering and technical trends were presented to improve single-well production rates in different demonstration blocks. High penetration rate of high quality reservoir is the fundamental basis for a high production rate, so gas bearing shale layers were first classified into four classes. Densities of natural fractures, heterogeneity of principal stresses and brittleness indexes were then evaluated to review qualification of fracturing treatments. Also, correlations were established between slick water volume, proppant volume, pumping rate and test production and the fracture-complexity index （FCI） was also evaluated through micro-seismic interpretation. The following findings were achieved. （1） The penetration rate of class I shale reservoirs is higher in the Changning block and when it reaches over 50 percent, production rates and estimated ultimate recovery （EUR） are estimated to be over 15× 10^4 m3/d and 8 000× 10^4 m3, respectively. （2） The Zhaotong block has a better qualification of fracturing treatments and the FCI is much higher, but because of low sand volumes and pumping rates, its test production rates are dissatisfactory. It is concluded that improving the penetration rates of class I shale reservoirs in the Zhaotong and Weiyuan blocks and optimizing the fracturing parameters in the Zhaotong block should be our targets in research to further increase the production rates of horizontal shale gas wells in the three demonstration blocks.