A series of tests were performed on a manually fractured (subparallel to bedding) and propped (using quartz sand) shale plug to determine the extent to which the proppant fractured and the effect the proppant had on the fracture wall when subjected to reservoir conditions. The specimen was repeatedly subjected to reservoir conditions of 20.7 MPa confining pressure, 6.9 MPa differential stress and a temperature of 75°C. While at reservoir conditions the sample permeability was measured. Periodically the specimen was removed from the test system and scanned with a X-ray micro computed tomography machine to visualize the fracture and proppant. Noticeable decrease in flow was observed with subsequent testing due to fracture closure. This can be attributed to observations of clay swelling, proppant embedment/fracture, and shale wall spalling leading to a decrease in effective fracture aperture. Flow induced particle transport clogged flow paths and impeded flow. It was observed that isolated grains tended to crush whereas continuous grain patches tended to fracture with little displacement and tended towards embedment.
In recent years the United States has become the largest producer of both petroleum and natural gas. This is a direct result of source rock exploitation through drilling and hydraulically fracturing long horizontal bore holes. While there is no dispute that this process has been effective and profitable there is still much that is not well understood about the life of proppants and fracture connectivity downhole. Production declines from these sources are higher than conventional wisdom predicts. Therefore, it is important to better understand the fracture and proppant placement process so that it can be tailored to help maximize production while minimizing environmental impact.