Abstract: Reservoir Sand Production; Its Relationship to Environments of Sedimentation and Diagenesis

Bernabe Aguado

Oil production in the Boqueron Field has been dampened by the high amount of sand produced. This field, located in the Eastern Venezuelan basin, has had a irregular development: out of the eleven wells drilled two have been abandoned due to the sand plugging and only five producing wells do so with high but maneuverable amounts of sand. This fact has reduced the reservoir recoverable reserves to 9% of the original oil in situ. Sedimentological and petrographical analysis of three cores has allowed us to determine fluvial to nearshore environments of deposition within a major transgression. The sediments related are characterized by clean, medium to fine grained sands in the fluvial channels and bioturbated, clayey sands for the transgressive bars. The diagenetical history imprint on t ese rocks differ by the presence or absence of clay matrix, which acted as an inhibitor for the precipitation of quartz cements, thus the fluvial sands are well cemented while the marine bars have a clay film around the grains that prevented such cementation. This renders the producing interval to be highly heterogeneous with respect to rock strength, fact that is readily seen in the Wellbore Stability log and in the drilling time reported for the cutting of the cores. Since this reservoir is at a depth of 16000 ft. Once the wells are put into production, the fluid pressure easily overcomes the rock strength in the clayey sands, fracturing the rocks and carrying the fragments along with the fluids produced. In this case, rock strength is ultimately controlled by the environments of depos tion; therefore, simple sedimentological correlations throughout the reservoir can be used to predict "weak" intervals and areas, which can be avoided during field development.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994