Abstract

There contains a large number of natural gas resources in Northeast Sichuan region of China where the SINOPEC has discovered two large gas fields in Puguang and Yuanba Area. These gas fields are characterized by deep buried depth, high formation pressure (equivalent density reached 2.5g/cm3), high hydrogen sulfide and carbon dioxide content (15.16% H2S content and 8.64% CO2 content in Puguang gas field) and multiple formation pressure system distribution. Especially in the upper continental formation, the drilling job is very hard to carry out for high formation pressure, high rock abrasiveness and stratum fracture development. The prominent problems include low rate of penetration, frequent circulation loss, horizontal well trajectory control, well control hazards and poor cementing quality etc. By applying the integrated matching technologies, such as well bore structure optimization, air/N2/foam drilling and composite drilling techniques, the ROP is substantially increased. Some measures such as plugging while drilling, bridging plugging and chemical gel plugging technologies are developed to solve the complex formation leakage problem. Cement quality has improved through the application of gas channeling prevention slurry and anti-acid gas corrosion slurry. The ultra-deep horizontal well drilling technologies also have become key technical method for the development of high-sour gas field. Since 2005, more than 100 wells were drilled with 100% success ratio.

Foreword

Sinopec has gained a series of natural gas exploration achievements in the Northeast Sichuan Basin of China. The Puguang gas field is the first large un-compartmentalized high-sulfur marine gas reservoir which is a model of efficient exploration at domestic in recent years, and Yuanba gas field as well. These regions have complex geology conditions and the formation characteristics are as follows: First of all, gas reservoir is deeply buried, the geological structure is complex where distribute both continental and marine formations, the continental formation accounts for over 65% of total depth. Next, the lithology of continental formation is tight, the rock is abrasive and the drillability grade in most formations is great than level 6. Thirdly, the formation pressure system is complex, and there are several different pressure gas-bearing beds where the pressure equivalent density reaches to 2.5g/cm2, and the marine formations in some regions also contain high-pressure salt-water or evaporite formations. Lastly, marine formations are characterized with high heterogeneity, high content of hydrogen sulfide and carbon dioxide. The H2S contentis 15.16% and CO2 content is 8.64% in Puguang gas field while 5.75% H2S and 9.58% CO2 in Yuanba gas field.

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