| Turkmenistan is the world’s fifth-largest natural gas resource country and natural gas is very rich, the total amount reach24.6×1012m3，Amu Darya area is the largest gas production area in Turkmenistan, in this area, fractures develop in carbonate reservoir, which provides a good storage space and seepage channel for oil&gas, but also lead that lost circulation frequent happened in this region, and large fracture vicious lost circulation often cause server blowout, using existing plugging technology to deal with these accdients is difficult.the success rate of plugging is too low, the plugging cycle is too long, the plugging materials loss too much, and always do great harm to the reservoir, which seriously affects the progress and economic effects of exploration and development. the reservoir lost circulation has become the region’s "bottleneck" of safety drilling technology.Therefore, developing a suitable plugging technology for the carbonate fractured reservoir in Amu Darya area is very necessary.On the basis of statistical analysis on core data, geological data and drilling&completing data, around the plugging technology establishment of carbonate fractured reservoir in Amu Darya area, from plugging material optimization and sealing ability evaluation and so on. a large mount of experiments have been carried out systematically. Main recognition and results are as follow:(1) Lost circulations in the region are mainly concentrated in Callovian-Oxfordian carbonate reservoir, the key and difficult point for lost circulation problem is that the loss formation is also the reservoir at the same time, and the root cause is that the resistance capacity of formation is low and the safe window of drilling fluid density is narrow, based on the understanding, the way to solve the problem of lost circulation in this region has been put forward:based on the existing plugging mechanism, selecting suitable high-performance plugging materials for Amu Darya area, cooprate with related construction technology. through the synergies between plugging materials, forming a high strength and dense slug, stablly sealing the cracks, so as to enhance the resistance capacity of formation.(2) Guided by the existing mechanism, combined with the requirement for plugging materials of "the loss formation is also the reservoir" and enhancing the resistance capacity, three types of plugging materials that is suitable for Amu Darya area have been selected out-bridge plugging materials(calcite particle material, leite sheet material and leite fiber material), delayed expansion agent GWS-1and HHH plugging agent.(3) Studying on the loss volume and resistance capacity, on the basis of a large amount of plugging experiments, a formula that has good plugging effect has been gotten, which can seal3mm fracture on4MPa with the cumulative loss volume of no more than10%.The optimal plugging formula is:base slurry+5%calcite particle+2%leite sheet material+1%leite fiber-6%GWS-1+30%HHH+0.2%sodium pyrophosphate+0.1%NaOH+0.5%fiber+3%quartz sand+barite. the base slurry formula is:6%bentonite slurry+0.3%PAC-HV. The experiments results show that, the formula own strong adaptability for cracks, high resistance capacity, wide application range, and can be acid to dissolve, but the plugging slurry need to pump to the loss formation separately, so it needs to consider fully when constructing.(4) The field application of this plugging formula in Turkmenistan B well show that, the plugging formula make a good performance on dealing with the serious lost circulation problems of carbonate fractured reservoir in Amu Darya area, but the initial fluidity of plugging slurry is a little weak, which make it hard to pump, so further research is needed. |
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