Inferring Interwell Connectivity from Well Bottomhole Pressure Fluctuations in Waterfloods

Abstract

Abstract This paper presents a new procedure to determine inter-well connectivity in a reservoir based on fluctuations of bottomhole pressure of both injectors and producers in a waterflood. The method utilizes a constrained multivariate linear regression analysis to obtain information about permeability trends, channels and barriers. Previous authors applied the same analysis to injection and production rates to infer connectivity between wells. However, in order to obtain good results, they applied various diffusivity filters to the flow rate data to account for the time lags and the attenuation. This was a tedious process that requires subjective judgment. Shut-in periods in the data, which were usually unavoidable when a large number of data points were used, created significant errors in the results and were often eliminated from the analysis. This new method yielded better results compared to the results obtained when production data were used. Its advantages include: (1) No diffusivity filters needed for the analysis; (2) Minimal numbers of data points required to obtain good results; and (3) Flexible plan to collect data as all constraints can be controlled at the surface. The new procedure was tested using a numerical reservoir simulator. Thus, different cases were run on two fields, one with five injectors and four producers and the other with 25 injectors and 16 producers. For a large waterflood system, multiple wells are present and most of them are active at the same time. In this case, pulse test or interference test between two wells are difficult to conduct since the signal can be distorted by other active wells in the reservoir. In the proposed method, interwell connectivity can be obtained quantitatively from multi-well pressure fluctuations without running interference tests.