Cementing Unconsolidated Sandstone Formations with Coexisting Oil and Water

Abstract

Abstract Oil wells with unconsolidated formations where oil and water coexist require special attention during drilling, well completion and production stages. This is the case of a heavy oilfield located in the Neuquina Basin, Argentina, where for many years, periodic cement squeeze jobs were needed to avoid near-wellbore water channeling. In addition to formation unconsolidation, this reservoir has high porosity and permeability as well as poor lithologycal barriers. When the top of the oil producing zone is perforated and evaluated by swabbing, viscous oil carrying formation sand is initially produced. After a short period of time (days), water cut rises to values close to 100 % promoted by the high mobility ratio. This response impedes a profitable production of these oil wells. After analyzing open and cased-hole logs, as well as production history data, the hypothesis for the short term water invasion was identified as near-wellbore channeling caused by sand production. This process was aided by formation weakening due to its interaction with drilling and completion fluids. The solution to this problem was based on a primary cementing procedure that included specially designed slurries containing polymeric admixtures. Effective formation isolation, bonding and near-wellbore consolidation was achieved by allowing these additives to leak-off into the unconsolidated formation. This paper presents the experimental tests performed to develop the procedure and the field results obtained after five successful cementing jobs. Sand production was significantly diminished and no cement repairs were needed after the first six months of production.