| When the verage reservoir permeability is equal to or less than50X10-3um2,this reservoir is low permeability reservoir. The resources of low permeability reservoir were rich, which widely distributed at home and abroad.And it accounts for a high proportion of the domestic and international oil and gas production. However,there were much more problems durlling the development of the low permeability reservoirs, for example, technical difficulties and formation damage. Therefore, how to reduce the damage to oil, to effective reform reservoir, and to improve the low permeable oilfield efficiency, is play the vital role in our oil industry sustainable and stable development.Thus, this paper is focus on oil and gas layer protection technology during the drilling of low permeability reservoir in Lin’pan district. Core samples of the four wells were taken as object of study(they were Lin86-1well, Shang73-6well, Shang67well and Xia52-Geng412well). We studied on four respects of the core sample:reservoir potential damage factor analysis, reservoir sensitivity analysis, drilling fluid performance analysis and analyse of drilling fluid.This article first analyzed the potential damage issues in this district, which included the analysis of X-ray diffraction,Scanning electron microscope and Casting thin sections. We could obtains the following conclusion through the analysis:core samples’clay mineral content was between1.5%to2%, and the filling of clay minerals were less and the structure of clay was tightly. Furthermore, reservoir pore space and pore constriction were not well developed, reservoir space was relatively small and seepage ability was poor.Thence,the damage caused by clay hydration expansion and migration were lesser extent.After the analysis of the damage factors, then we studied the sensitivity of rock samples. The research process is basically on the basis of 《SY/T5358-2002Formation damage evaluation by flow test》. The results showed that:the speed allergy, water sensitivity, alkali sensitive degree of the study formation are weakly; all of three wells’ critical salinity were about6000mg/L. This was the same as the analysis results of the potential damage factors.According to the characteristics of protection on low permeability reservoir, we studied the rheology of drilling fluid and the compatibility of the treatment in laboratory. This part mainly according to the 《SY/T5621-93drilling fluid test procedure of treatment》 to test different drilling fluid and the correlation theological properties. Two kind of drilling fluid formula(MMH, MMH-nanometer emulsion drilling fluid system) were developed according to stratum characteristics of the Linpan district. Experimental results showed that MMH, MMH-nanostructure system had the characteristics of composition was simple, performance easy to control, filtration easy to control and so on. But part of the additives could react with formation water and produce precipitation. In order to better research the damage degree of the drilling fluid during the drilling operation, static and dynamic simulation damage experiments were did in the lab. This part mainly according to the 《SY/T6540-2002Lab testing method of drilling and completion fluids damaging oil formatioin》. Through the experiments results, we tried to find out the damage causes of the core samples in different mud systems. Experimental results showed that site mud and the scene MMH-nanometer emulsion system had a low damage on the core sample. And the permeability recovery value could reach to80%.It was good for reducing the damage degree when using of temporary plugging technology in mud system. Meanwhile the damage of low permeability reservoirs caused by mud system in Linpan was shown aslight surface damage which was under the elimination range of perforating measures.We could get the conclusion through the related research that the filtrate damage was effectively controlled due to the small reservoir permeability, small core pore throat, the low possibility of solid phased particles invaded of the core. Plus the good control of the filtration which could make sure the invaded depth was light. Comprehensive all above factors we could get the final conclusion that MMH-nanometer emulsion system had a good protection effect on low permeability reservoir.Furthermore, inspection the effect of the drilling fluid through field test. The test well (Xia503-53Inclined well) drilling fluid performance informed that the MMH-nanometer emulsion system had a good rheology performance, water loss was easy to control and had a good effect on reservoir protection. Dynamic damage experimental results showed that after using the relevant reservoir protection measures the recovery of reservoir permeability was improved and the damage showed as light surface damage. After removed the pollution plug the permeability recovery value could reach to91.2%. After comparison with the test well Xia503-53Inclined-well, the production is higher and month attenuation extent was small which reach the design purpose. |
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