The Department of Energy's (DOE) Natural Gas Resource and Extraction Program consists of industry/government co-sponsored research, development, and demonstration (R&D) projects, which focus on gas recovery from both conventional and nonconventional resources. The Drilling, Completion, and Stimulation (DCS) Project focuses on advanced, non-damaging technology systems and equipment for improving gas recovery from conventional and nonconventional reservoirs. As operators move from development of current day economically attractive gas-field development to the lower permeability geologic regions of domestic onshore plays, increasing the emphasis on minimum formation damage DCS will permit economic development of gas reserves The objective of the Project is to develop and demonstrate cost-effective, advanced technology to accelerate widespread use and acceptance of minimum formation damage DCS systems. The goal of this product development effort is to reduce costs and improve the overall efficiency of vertical, directional, and horizontally drilled wells in gas formations throughout the U.S.
The current focus of the Project is on the development of underbalanced drilling technology and minimum formation damage stimulation technology concurrently with the appropriate completion hardware to improve the economics of domestic natural gas field development. Ongoing drilling technology projects to be discussed include development of an electromagnetic measurement while drilling system for directional and horizontal drilling in underbalanced drilling applications and the development of a steerable air percussion drilling system for hard formation drilling and improved penetration rates. Ongoing stimulation technology projects to be discussed include introduction of carbon dioxide/sand fracturing technology for minimal formation damage.
Formation damage may be caused by several factors related to production including, filtrate invasion, drilling and completion fluid penetration into the formation, and formation clay structural expansion. A common cause of formation damage is permeability reduction. This reduction is typically attributed to pore plugging from migration of native clays, formation of precipitates, and injection of fines or solid particles. This paper deals specifically with prevention of formation damage related to well drilling and stimulation practices in naturally fractured formations.
Naturally fractured formations experience near well-bore formation damage due to fluid loss during the horizontal drilling process. Typically the producing formations and natural fractures are exposed to damaging drilling muds and related additives for an extended period of time as the horizontal well is being drilled. Filtrates and aqueous solutions may penetrate the pore space or natural fractures if the well is drilled overbalanced (to control gas influx drilling fluids penetrate the formation due to lost circulation and fracturing). Water based muds may cause fluid imbibition and capillary retention, impeding the removal of production fluids from the formation; thus, causing a zone of damage around the horizontal wellbore. One option for avoiding formation damage during the drilling process is the use of low density air/inert gas, air-mist, foam aerated/nitrified mud and underbalanced muds as the drilling fluid. These fluids enhance rock cutting removal while avoiding fluid invasion problems due to lost circulation or migration of fluids into the formation due to pressure overbalance between the fluid column and the rock pore pressure. The creative selection of numerous alternative underbalanced fluids beyond the current mud versus air options should be developed.
Formation damage related to the stimulation process is usually associated with fluid selection and the impact on the producing reservoir rocks. A recent survey of the petroleum industry indicated that 51% of operators have stimulation problems associated with formation damage prevention or remediation. More specific problems listed contributing to this formation damage were breaker problems with gels, non-compatibility with formation rock, and water retention problems.