Scale inhibitor squeeze treatments in unfractured reservoirs can be readily simulated in matrix flow models, designing such treatments for application in fractured reservoirs is less routine. One reason for this is that the flow process and transport mechanisms by which the inhibitors are retained in fractured formations differ considerably from simple matrix flow. In previous papers, we described a diffusion-controlled transport model for scale inhibitors in low permeability fractured reservoirs where little matrix flow is expected. In this paper, the model has been used to simulate squeeze treatments performed on multiple wells in a fractured shale formation and compared to simulations using a matrix flow model.
A number of squeeze treatments were performed on wells in a fractured shale formation yielding long treatment lifetimes. The squeeze treatments were designed using a matrix flow model. Calculations indicated the design pumping rate would require an injection pressure significantly more than the fracture pressure for the formation indicating little matrix may possible for this case. The treatments were successful, however, the observed field return did not match the prediction and in some cases longer treatment lifetimes were observed.
When a standard matrix flow model was used, the resulting field isotherms were significantly different for each well in the formation. This is taken to indicate that the matrix flow model approach is not accurately mimicking the field data. When the same data was examined using the diffusion based fracture model, a single isotherm was found to be a good match for all of the wells from the formation. In addition, explicitly modelling the varying water production rates in the diffusion model gave good correlation with changing trends in the return concentrations seen in the field return. Furthermore the possibility of improving the treatment lifetime is considered, factors such as the effect of the overflush volume and injection rate are discussed as treatment modifications and the influence may have on formation damage.
Accurate prediction of squeeze treatment lifetimes is important for scale management both economically to ensure optimum productivity and practically to schedule treatments appropriately. Until recently this has not been achievable for fractured formations without the use of full field simulators. The paper illustrates that an appropriate near wellbore model can give good agreement with field data and has been used to design better treatments without the need for complex full field simulators.