Abstract
MRC (Maximum Reservoir Contact) wells with extra-long laterals (formation contact length＞5000m) are drilled in many oilfields in the world to develop tight and thin reservoirs. LEL (Limited Entry Liner) completion and acidizing are an effective technology to stimulate these wells because they distribute the acid uniformly along the long laterals. The design of a distribution of holes in LEL is the key to this technology, especially for reservoirs with high heterogeneity.
This study focuses on the optimization of the current LEL completion design strategy by considering the porosity heterogeneity along the lateral and the permeability anisotropy within each segment. Firstly, a model for designing a distribution of holes in LEL is established by incorporating a newly developed model for calculating a post-stimulation equivalent skin factor. Secondly, three LEL completion design strategies are proposed: uniform acid coverage, uniform wormhole length and uniform equivalent skin factor. Thirdly, a real well case is introduced to show the difference between the three strategies in terms of the distribution of holes, generated wormhole length and post-stimulation skin factor.
In our new design model, the variances of formation porosity, the differences in acid outlet flow velocity among different segments and the difference in permeability in different directions are considered. This model is used in a horizontal well to achieve uniform post-stimulation equivalent skin factor and the result is compared with those by the other two design strategies. The result from the uniform acid coverage strategy shows that the total number of holes is 198, the length of the generated wormhole is 4.46ft and the equivalent skin factor is -2.88. The result from the uniform wormhole length strategy indicates that fewer holes (totally 135) and a more irregular holes distribution are obtained; the wormhole length is 0.43ft. The result from the uniform equivalent skin factor design strategy shows that the total number of holes is 161; the wormhole length and acid coverage are bigger at the heel but smaller at toe. It also shows that the equivalent skin factor is much bigger (even positive at the heel) than in the other two strategies, which indicates that more acid and consequently more holes should be added at the heel. It is also recommended for an appropriate selection of the three design strategies.
Our work is an optimization for LEL completion design based on the current design strategy in the industry, which only aims for uniform acid distribution. A guideline chart of the three design strategies we have proposed is also useful for engineers to select the appropriate LEL design methods based on the specific well conditions.
