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What Microseismicity Tells Us About Re-fracturing - An Engineering Approach to Re-fracturing Design
| Content Provider | Semantic Scholar |
|---|---|
| Author | Agharazi, Alireza Kashikar, Sudhendu |
| Copyright Year | 2016 |
| Abstract | Microseismic monitoring of re-fracturing of depleted horizontal wells frequently shows a concentration of microseismic activity at the heel area when no mechanical isolation is used. This observation indicates a localized stimulation of the well at the heel area, which potentially leaves a considerable length of the well unstimulated toward the toe. Different completion techniques, ranging from injecting diverters to using mechanical intervention methods, are usually used to avoid the localized stimulation and to enhance the treatment effectiveness. However, often overlooked is the effect of the reservoir rock’s mechanical characteristics on the treatment efficiency. We studied the geomechanics of re-fracturing and ran a series of numerical simulations to investigate: i) the effect of pressure drop along the lateral, ii) diverter effectiveness, and iii) the possibility of creating new transverse fractures from new perforations. For common casing diameters and fracturing fluids the pressure drop along the lateral is high and can result in a considerable pressure contrast of a few thousand psi between the heel and the toe. This results in the dilation of pre-existing fractures at the heel under the higher injection pressures developed in that section. In the absence of effective diverters, this condition persists throughout the treatment and gives rise to localized stimulation of the well limited to the heel, as observed by the concentration of microseismic events toward the heel. Our study indicates that the dominant stimulation mechanism during the studied re-fracturing treatments was the shear slippage of natural fractures by a pore pressure-driven mechanism, as opposed to creation of new transverse fractures from the new perforations. This conclusion is consistent with the observed long delay in microseismic response to the treatment and also with the observed increasing trend of the treatment pressure with pumping cycles. Based on these findings, we developed an alternative re-fracturing method that aims at increasing the reservoir effective complexity and enhancing the conductivity of the pre-existing hydraulic fractures uniformly along the well. The proposed method consists of a prolonged low-pressure and low-rate pad stage to pressurize the reservoir, followed by a high-pressure injection stage to stimulate natural fractures and place proppant in the new fractures. Critical to the success of this method is to avoid a high pressure contrast along the well, which can be achieved by proper selection of injection pressure and fluid viscosity with respect to the reservoir stresses and pressures along the well and the well characteristics. Numerical simulations indicate that the proposed method can considerably enhance the efficiency of re-fracturing treatments, at no additional cost compared to the common re-fracturing methods. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://msi-images.s3.amazonaws.com/HFJ_Refrac_January-2016.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
