Tip Screenout Fracturing: A Technique for Soft, Unstable Formations

TLDR

Soft, unstable formations have been targeted by various stimulation methods, including acid–proppant treatments that leave sand‑filled channels, but short, high‑conductivity fractures are needed for many such reservoirs. This study proposes a tip‑screenout fracturing technique that uses only normal sand fracture procedures to treat soft formations where acid is ineffective or undesirable. The method screens out the fracture tip with sand, pumps slurry to widen the fracture, and packs it with proppant to achieve high conductivity, relying on prefracture tests to determine design variables and a theoretical schedule that is validated against pressure data and production from two North Sea chalk wells. The theoretical model aligns with fracture pressure measurements and production results from two completed wells, demonstrating the technique’s effectiveness in Upper Cretaceous chalk.

Abstract

Summary Several special stimulation techniques have been proposed for soft, unstable formations. One example is a combination of acid and proppant, which leaves the acid channels full of sand. This paper discusses an alternative completion technique that involves only normal sand fracture procedures and is effective where acid is ineffectual or undesirable. Because the procedure is aimed primarily at creating short, high-conductivity fractures in soft formations, its use can be extended to any formation where such a treatment is practical and economically feasible. The fracture design is based on intentionally screening out the tip of the fracture with sand and then continuing to pump slurry to increase the fracture width and to pack the fracture with proppant to obtain high conductivity. Because this involves severe risk of a premature screenout, and because failure to achieve the tip screenout will not yield the desired stimulation, special prefracture tests are required to determine fracture design variables. The implementation and analysis of these tests are discussed, along with the theory behind the fracture design schedule. This theory is then compared with fracture pressure data and production performance from two wells completed in an Upper Cretaceous chalk formation in the Norwegian Sector of the North Sea.