Fracturing unconventional formations to enhance productivity (original) (raw)

Unlocking the potential of unconventional gas reservoirs would change the balance and future of the oil industry. Unconventional gas reservoirs may be tight gas, CBM, or shale reservoirs. Economic production of any of these three types requires the creation of multiple fractures from a long horizontal well. Fracturing horizontal wells brings a host of issues from the rock mechanics, change of stresses around the created fractures and fluid flow. New as well as re-interpreted laboratory experiment shed new light on fracturing a horizontal well and the effect of how the well is completed on the fracturing process. The results may explain the presence of multiple fractures at the wellbore that was sometime observed. The geomechanics issues would influence the fracturing process especially in naturally fractured formations. The paper will also investigate the effect of various fracturing scenarios on the stress distribution around the fractures. Optimization of the number of fractures is another issue that is investigated in this paper using both fluid flow and geomechanics aspects. A special attention to shale formations is given. We do that for two reasons; first, because of the great potential of shale formations, and second, because the special shale characteristics that make shale unique and challenging. Shale formations have ultra-low permeability that may be in the nano-darcy range, they are naturally fractured, and depending on the carbon content, they may have a significant amount of adsorbed gas. This paper will also investigate the effect of gas adsorption on productivity and diagnostic testing. Field examples will be also presented.