Evaluation and Selection of Drill-ln-Fluid Candidates To Minimize Formation Damage

Abstract

Summary Conoco drilled and completed a horizontal well in a depleted, high-permeability oil reservoir. The formation is an unconsolidated, clean sandstone with absolute permeability over 3,300 md. The unconsolidated nature of the formation combined with its low pressure and high permeability caused concerns regarding hole stability, fracturing, excessive fluid loss, and differential sticking. To identify the best drill-in fluid (DIF) for the horizontal section, the evaluation of fluid candidates focused on both drilling properties and formation/completion-damage potential. The testing compared fluid performance in standard drilling-fluid tests, low-shear rheology at elevated temperature, dynamic fluid-loss behavior at elevated temperature, and core-flow tests. The flow testing was performed with cores from an offset well to simulate damage caused by DIF exposure and to evaluate remedial treatment options. Also, a new laboratory-scale procedure was developed to observe the tendency of prepacked screens to be plugged by DIF filter cake and unconsoli-dated formation sand. In addition to the laboratory testing, a review of the drilling and completion operations is presented, including performance of the drilling fluid at high overbalance pressure ( ≈ 2,600 psi) and the design and execution of subsequent remedial treatments. The production history is discussed and related to laboratory observations regarding cleanup and remedial-treatment effectiveness.