The Xujiahe gas reservoir located in the south of Sichuan Basin is a vital exploration and development field of Sinopec Corp. in south of China. The clasolite sandstone physical properties of Xujiahe formation is low porosity, low permeability and poor pore throat construction. Furthermore, the naturally fractured sandstone formation is characterized with strong heterogeneous, ultra-high compact and ultra-high pressure. High density drilling fluids(more than 2.9) were used because of the poor drillabillity and the high formation pressure. Meanwhile, the high density drilling fluids and the long soaking time in the well bore caused serious damage to the formation, which lead to nearly no production during the productivity test of gas wells. Initially, the high treatment pressure (maximum pumping pressure is about 95MPa) and nearly no sucking in formation lead to the failure of allconventional acidzing and hydraulic fracturing treatments. Through the formation damage mechanism experimental study and delicate diagnosis, the quantitative description of the damaged depth and degree, the tremendous damaged depth of which most of wells exceed 10m is proved to be the main reason to the failure of the conventional acidizing in this field. After further optimized stimulation treatment study, a novel stimulation of which the high density and deep penetration perforation, oxidation acidizing combined with deeply network acidizing in naturally fractured formation is put forward. Two treatments have been applied in Xujiahe gas reservoir successfully. The stimulation treatment results are very satisfactory. The steady gas output of Well G10 was increased to 8.95?10 4 m3/d(AOF:26.4?104 m3/d) from the 765 m3/d, and the skin was decreased to ?4.72 from 17.15 after stimulation treatment. This provides an optimal integrated stimulation for gas wells to be put into production in the field.
The Xujiahe gas reservoir in the south of Sichuan Basin, with pressure coefficient of 1.11–1.45 and depth of 2250.0-2350.0m, is the key exploration and exploitation block of Sinopec. As the serious slurry damage during drilling, production test shows little productivity; contrary to the analysis results from geology, logging, core analysis, well drilling & completion datum, and reservoir stimulation is necessary for the economic yield. In previous time, acidizing and hydraulic fracturing are adopted, but both of them are failed as the high executing pressure and the fluid hardly come into the formation. Therefore, proper stimulation technology for this gas reservoir must be determined to ensure the success and roundly prompting the gas reservoir exploration and exploitation.
In allusion to the characteristics as serious damage, micro-fracture growth and high fracture pressure et al. the tightened gas reservoir has, surrounding the discussion on reservoir stimulation strategy, formation damage evaluation, acid system as well as attached acidizing technology, develop large scale deeply acidizing technology including diagnostic analysis of formation damage, acid system with lower damage, lower friction, high retardation and easily flowing back, optimal design et al. This paper described these researches as well as a successful case study in G10.
