Taking Advantage of Sweet Spots of MFHW’s
By: Saad Ibrahim, P. Eng (Jan. 10, 2022)
Multi-stage Frac of Horizontal Wells (MFHW’s) has become the main technique used in tight and unconventional reservoirs. It is expensive to, drill, frac, and complete MFHW’s. Therefore, production optimization has become essential to make technical and economic sense of implementing MFHW’s. There are several production optimization techniques are commonly used including:
- The length of the lateral.
- Drilling and completion method; open hole vs cased hole.
- The optimum number of frac stages.
- The optimized size of the frac’; the proppant tonnage used per stage
- The selection of the placement of frac stages, and taking advantage of the sweet spots present along the lateral.
Because of the extensive subject optimization parameters mentioned above, the discussion in this short article will be focused on the last parameter; Taking advantage of the sweet spots present along the lateral.
How to locate the sweet spots?
- Open hole logs (Gamma-ray, density/neutron, etc.)
- Drill cuttings
- Mud gas detection
- Advanced seismic interpretations
Whether the well is open-hole or cased-hole competed, it is highly beneficial to selectively place the frac stages where the best reservoir quality is expected (sweet spots).
How to quantify the benefits of sweet spots?
A numerical model (Kappa/Topaz) is used showing the average perm of 0.1 md and a sweet spot of 2.0 md. Three cases are investigated for a gas reservoir:
A summary of the three cased is in the table above.
- Case 1: Missing the sweet spot of 2 md, in a cased hole completion, resulted in the lowest gas recovery of 57.6 MMscf after 3 yrs of production
- Case 2: Positioning a frac stage at the sweet spot of 2 md, in a cased hole completion, increased gas recovery to 113 MMscf after 3 yrs of production
- Case 3: Positioning a frac stage at the sweet spot of 2 md, in an open hole completion, maximized the gas recovery to 159 MMscf after 3 yrs of production
- Taking into consideration the sweet spot and well completion type and design the frac stage location is very beneficial