Abstract
Out-Of-Sequence Pinpoint Fracturing is a conceptual way of maximizing reservoir contact by creating fracture complexity via reducing or neutralizing the stress anisotropy to improve fracture conductivity and connectivity. A complex fracture network is formed by activating planes of weakness present in the form of natural fractures, fissures, faults, joints, and cleats. Branch fractures are created due to the induced stress-relief fractures where they can be connected to the main bi-wing hydraulic fractures to improve fracture network connectivity. Out-Of-Sequence Fracturing is initiated by fracturing Stage 1 (at the toe) and then fracturing Stage 3 toward the heel. Once a desired degree of stress interference between the Stages 1 and 3 (Outside Fracs) is established, Stage 2 (Centre Frac) is placed between the Outside Fracs. The Centre Frac enhances fracture network connectivity and conductivity by connecting to stress-relief fractures from the outside Fracs, taking advantage of the altered stress state.
Out-Of-Sequence Fracturing has successfully been tested in Western Siberia (by LUKOIL) and Western Canada in 2014 and 2017, respectively. A fracture model is calibrated using treatment pressures and instantaneous shut-in pressures (ISIP) from the Out-Of-Sequence Pinpoint Fracturing in Western Canada. The fracture model is coupled with reservoir simulation and RTA to evaluate the production potential in Out-Of-Sequence Pinpoint Fracturing and to conduct an extensive sensitivity analysis on petrophysical/geomechanical properties (stress anisotropy, Young's modulus, Poisson's ratio, process zone stress (PZS)/net extension pressure, fracturing gradient, and matrix permeability) and treatment variables (stage spacing, treatment fluid volume/viscosity/rate, and proppant tonnage/size/concentration) to identify the factors that are most critical to optimizing the treatment.
The results reveal noticeable production uplift from a carefully designed Out-Of-Sequence Pinpoint Fracturing, which avoids excessive fracture complexity that impedes fracture growth due to pressureout and screenout. Out-Of-Sequence Pinpoint Fracturing is most sensitive to stage spacing, treatment rate, proppant and fluid intensity for the Centre Frac, stress anisotropy, PZS, and brittleness factor (combination of Young's modulus and Poisson's ratio). Screening of these parameters helps identifying well candidates and treatment strategies to avoid both insufficient fracture complexity and excessive fracture complexity, where higher-than-anticipated treatment pressures are observed as an evidence of shear fractures being filled with treatment fluid, causing an additional component of stress that must be opposed by treatment fluid, realizing that higher pressures are only a risk when they are higher than surface pressure constraints.
This is the first attempt in pressure history-matching and screening for formation properties and treatment strategies for maximizing Out-Of-Sequence Pinpoint Fracturing benefits. The learnings from this multi-faceted study guide future successful designs of the Out-Of-Sequence Fracturing for completion optimization in unconventional and conventional reservoirs. Rendering a full-length interference effect is possible by conducting an optimized Out-Of-Sequence Fracturing in multiple wells (as part of large-scale field developments) to ensure optimizing the stress shadowing while reducing the risk of well bashing.
