Laboratory Evaluation of Formaton Damage Impact of Drill-In Fluid Lubricants in a Low-Permeability Sandstone Gas Reservor

摘要

Conventional lubricant products composed of different surfactant materials are required in water-based mud for drilling highly deviated and horizontal pay zone sections due to their lubricity associated with torque reduction and better penetration rate. Drill-in fluid (DIF) filtrate-induced formation damage in low-permeability gas reservoirs as a result of water blockage and reduced relative permeability to gas can be significant in view of the high capillary pressure associated with small pore throats. Formation damage risk assessment of the drilling lubricants utilization was therefore considered critical for a low-permeability gas reservoir development project. Lubricant product evaluation experiments were designed to provide the production impairment potential measurements using Berea and Unayzah sandstone cores with a laboratory formulated DIF and base brine containing 3-4% lubricant by volume and to confirm fluid compatibility with divalent salt (CaCl2) brine. Fluid compatibility and emulsion risk was investigated using mineral oil as the representative formation hydrocarbon fluid. Core flood and dynamic filtration tests were carried out at an estimated bottom-hole temperature of 250 °F and pressure of 1,000 psi for the high-temperature reservoirs while the compatibility tests were carried out at room temperature. Filter cake removal tests were also performed by using high pressure, high-temperature filter press equipment and synthetic disks to determine filter cake removal efficiency with acid brine breaker fluid. The obtained results from the laboratory study were integrated to evaluate and rank the lubricants based on their assessed formation damage risk. The test results showed that both lubricant return permeability and compatibility tests were important in selecting the best performance lubricant. This paper discusses the experimental analysis of the formation damage potential of 12 commercially available water-based mud (WBM) lubricants. It also provides an insight into the formation damage (FD) impact of the drilling fluid lubricants on gas reservoir deliverability.