| With worldwide energy demand for natural gas is increasing, the ratio of conventional natural gas production and storage reservoirs are showing increasing production decreased, unconventional gas resources are considered as the most promising energy supplement, and therefore low permeability gas reservoir exploration and development draw more and more people’s attention. Experts have been proposed natural gas resources in China is about to be discovered in more than50%of the gas exists in the tight reservoir In the evaluation of resource onshore, so low permeability gas reservoir has gradually become the main source of natural gas in our country. Therefore, efficient exploration and development of low permeability reservoir is extremely important practical meaning on the storage of oil production growth of China.DF1-1gas field is the biggest proprietary gas field of CNOOC (China) co., LTD. Zhanjiang branch, which is located in the northern gulf of the south China sea Yinggehai sea area and about100km from Yinggehai town of Hainan province, about113km from the Dongfang county. The water depth is about70meters. The reservoir belongs to Sec. Ymggehai group and the main reservoir is divided into I, II, III gas group. The large-scale development of DF1-1gas field began from the first-stage project in2002. During the2002-2013years, it carried out the first-stage project, the second-stage project and the subsequent adjustment well, mainly developing II and III gas group. So the relevant research on DF1-1gas field is mainly focused on II and III gas group, rarely comes to I gas group. This comprehensive adjustment project plans to drill33development wells which16wells in I gas group, accounting for48.5%of the project. Therefore, the I gas group reservoir as objects, paper studied the basic geological characteristics and damage mechanism of low permeability reservoir, analyzed the physical characteristics, reservoir characteristics and damage factors of I gas group reservoir, and according to the findings proposed the corresponding drilling and completion fluid optimization system.Through the system analysis and experimental research, got main results and understandings, as follow:(1) Research and summarize the factors of low permeability reservoir damage. Water lock, reverse wetting, emulsifying blockage, liquid incompatibility sensitivity damage, blockage of water-soluble polymer adsorption and solid particles blockage are major factors in low permeability reservoir damage occurred. In terms of open hole completions, the ideal system to protect low permeability reservoir drilling fluid film is no solid phase drilling fluids.(2) Describes and analyzes the I gas group permeability reservoir characteristics and damage factors. I gas average porosity is22.2%, with an average air permeability of3.471mD. I gas has the middle porosity and low-ultra low permeability, clay mineral content is high, the average content of clay minerals is23.4%, the expansion is strong; reservoir of I gas with a strong-extremely strong water sensitivity, middle-strong speed sensitive, alkali sensitive is weak, acid sensitive is non-weak; sensitivity of rising salinity fluid is non-weak, water lock effect in Ⅰ gas reservoir had significant damage; hydration of clay and water-soluble polymers I gas in reservoir have significant damaging effect; water-sensitive, water lock, hydration clay solid phase, a water-soluble polymer is the main damage factor of I gas reservoirs.(3) Research and select waterproof locking agent SSJ which has resistance to temperature and salt and can increase the surface tension at0.2%amount to less than25mN/m. SSJ could significantly reduce water blocking damage, which is better than waterproof locking agent used in the second-stage project.(4) Optimize the formula of PRD drilling fluid:for removing the harmful solid phase and protect reservoirs, the macromolecules Plus has been introduced in the original system with amount of0.1-0.2%, improved the original PRD drilling fluid flocculation ability. The inhibition, anti-swelling property and particle size distribution results of the new PRD drilling fluid also confirm this effect.(5) Optimizes the formula of chelating acid completion fluid and gel breaking liquid.Completion fluid formulation:filtered sea water+2.5%HCS+0.4%HTA+1.0%CA101-3+0.1%SSJ.Gel breaking liquid formulation:filtered sea water+5%JPC+2.0%CA101-4+0.1%SSJ.(6) The optimized drilling and completion fluid have excellent reservoir protection effect and compatibility. Polluted by the gel breaking liquid and chelating acid completion fluid, core permeability recovery value is over100%; simulated conditions of open hole completion, the polluted core permeability recovery value is over90%. |
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