Drilling and Gravel Packing with an Oil Base Fluid System
Authors: Methven Norbert E. , Kemick Jerome G. 
Published: December 2007

Formation damage usually is attributable to fluid systems that contain clay or significant amounts of water. Field experience, as well as laboratory studies, indicates that this damage can be avoided through the use of an oil-asphalt fluid system for drilling, completing, and gravel packing.

Introduction
The technology of sand control by gravel packing has been significantly advanced since its inception almost a century ago. This advancement has been primarily in completion design and placement techniques. Nonetheless, the success ratio of the gravel pack treatments is still far from ideal, as evidenced by well failures in many parts of the world. For example, according to a survey in offshore Louisiana, about 22 percent of the wells are production deficient and 23 percent are off production. Also, in the same area, there are over 30 workover rigs being used primarily for repair of sand control measures. It is apparent that future advancements in sand control technology will come from study and improvements of the entire drilling, completion and production system. These advancements should bring substantial rewards to the operator.
When we view the over-all system, we find that for controlling formation sand a fundamental requisite is the prevention of disturbance and rearrangement and the prevention of formation productivity damage during the drilling, completion productivity damage during the drilling, completion and production operations. This is borne out by the fact that the failure of sand control measures can invariably be traced to movement of formation particles up to, into, or through the formation restraining media. To prevent movement of these formation particles, considerable effort justifiably has been applied to precise placement of sand control measures. Unfortunately, placement of sand control measures. Unfortunately, well failure may already have been precipitated by other facets of the drilling and completion process. Thus, we need to identify these damage mechanisms and their physicochemical, capillarity and elasticity relationships in order to improve sand control.

Damage Mechanisms Drilling and Completion
From the outset, the drilling process causes elasticity changes in the drilled formation. Certain elasticity changes are unavoidable because of the very presence of a hole in an elastic medium. However, changes in elasticity, physicochemistry and capillarity that ordinarily are avoidable often are precipitated by formation damage caused during drilling and completion.
It is recognized that damage mechanisms are related to fluids that invade and/or react with the formation. These damaging fluids usually include aqueous phases that may cause the following:
swelling and hydration of in-situ clays, dispersion of insitu clays, capillary phenomena or water blocking, migration of clays from fluid formulations, insoluble mud cakes, particle tilting, nongauge, wellbore, and unstable wellbore.

Swelling and Hydration of In-Situ Clays
All clays absorb water molecules on the surfaces and edges of individual particles. In addition, the montmorillonites, mixed layer clays and certain illites can hold large amounts of interlayer water. Thus, when aqueous fluids are used in drilling or completing operations, clay swelling can occur. These swollen clays plug flow channels and impair well productivity. plug flow channels and impair well productivity. JPT
P. 671