A recent trend in the productive life of certain wells with frac- pack sand-control completions has shown a greater decline in performance than normal or expected. In many cases, this abnormal decline, both initially and long term, can be attributed to loss of conductivity in the proppant pack. Because conductivity is the major design criterion for frac-pack completions, it is imperative-to attain the maximum sustained production-that conductivity be optimized in the original completion and then maintained throughout the life of the well. The two major parameters of fracture conductivity are proppant permeability (size) and fracture width. Proppant size, to this point, has been largely dictated by Saucier's1 studies that suggested that the proppant size be as large as 6 times the average formation grain size to accomplish sand control in unsteady flow conditions. More recent studies2 have shown that it is acceptable to increase the proppant size by 8 to 10 times the formation grain size for frac packs only. In general, fracture length and width have been addressed within the sand-control community with the use of tip screen-out designs, facilitating treatments to gain additional net pressure and generate more propped fracture width. Recent testing with weaker and unconsolidated cores, however, shows that intrusion of the formation into the proppant pack causes substantial loss in measured retained pack conductivity. The testing also shows that a substantial amount of conductivity loss occurs due to interactions at the proppant pack/formation interface, even at low closure stress. In addition, the amount of damage increases as closure stress increases. Any movement and migration of the formation material into the proppant pack subsequently lowers the pack's conductivity. Thus, when frac-packing in weaker and unconsolidated environments, enhanced treatment materials and designs must be used to help ensure that frac-pack conductivity is optimized initially and maintained longterm. Different techniques have been tested and are showing real promise in maintaining long-term conductivity.
A great analogy for a fracture in a hydrocarbon producing or injection reservoir is that of a "super-highway." When the highway first opens it has 10 lanes running from the formation to the wellbore. However, as time goes by, those 10 lanes become 8 lanes, then 6 lanes, then 4, until the hydrocarbons are essentially flowing down a country road with backed-up traffic. Large numbers of hours are dedicated to developing a well plan that will allow maximum production over a long period of time, which calls for the maintenance of the "10 lanes of flow" described above. Until recently, there was no way to combat fines migration through the proppant pack to the wellbore. In the event that the formation includes the presence of laminated, highly heterogeneous, unconsolidated, compactable rock, the advent of fines could stymie the production of hydrocarbons from the well. This paper will discuss the high level of conductivity gained through the use of a surface modifying agent (SMA) currently being used in the Gulf of Mexico (GOM).
