This study presents a general method for analyzing pressure buildup data from a well located in a multiwell reservoir, especially in a special case of pressure buildup test which the testing well and adjoining wells are all shutting in at the same time. On this basis, the effect of multiwell interference on pressure buildup curve is analyzed. The method is obtained with the superposition principle, and is general in dealing with any combination of producing, injecting or shutting in conditions of testing well and adjoining wells. Pressure and the pressure derivative log-log new type curves are drawn up. Sensitivities of the type curves affected by different conditions of testing well and adjoining wells(producing, injecting or shutting in) and different parameters are analyzed, including the well spacing, ratio of the multiwell production and production/injection time, which are the main parameters that can reflect the interference of wells. It is shown that the multiwell interference exercises a significant influence on pressure derivative log-log curves of pressure buildup test. It can be summarized in following aspects: firstly, when the adjoining wells are producing, pressure derivative curves are in decline. Secondly, when the adjoining wells are shutting in, pressure derivative curves start to upward. Thirdly, well spacing has an influence on the time of interference on curves, and the ratio of the multiwell production affects the variability of the curves. Fourthly, the way to reducing multiwell interference impact on curves is made adjoining unchanged. Fieldcase buildup analyses in Sebei Gas Field which has a special case of pressure buildup test which the testing well and adjoining wells are all shutting in at the same time show the applicability of the new method, and the type curves had been validated by example. It is indicated that if the multiwell interference is not considered for well test analysis, it will lead to erroneous analyses especially in boundary identification. The novelty of the new method is in the ability to analyze pressure buildup test by different kinds of multiwell interference, and can obtain formation parameter more precisely.

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