A new method of completing multiple-layer tight gas wells is being investigated. The main concept is to place sliding sleeve valves in the casing string and complete the well with normal cementing operations. The sliding sleeves would then be opened one at a time to fracture layers independently without perforating. The possibility of high fracture initiation pressures is identified as the main risk with this approach.

This paper will discuss the theoretical and experimental study that was conducted to assess the viability of the cemented sliding sleeve concept by attempting to minimize and predict fracture initiation pressures.

Finite Element Analysis (FEA) was conducted to estimate the stresses in the cement and formation near the wellbore with sliding sleeve. FEA was used to adjust valve parameters that increased tensile stress in the cement and formation. Unstressed cement tests were then conducted on a variety of sliding sleeve valve shapes to verify the FEA study and to select the best valve shape.

Openhole and perforated casing fracture initiation pressures were calculated as a function of rock properties and far field stresses on the rock. An openhole condition was considered the best approximation to the opened sliding sleeve valve in regards to fracture initiation.

Full-scale stress frame tests were conducted using sandstone blocks with far field stress applied. The base case was set up using 4-1/2-in diameter casing cemented in one block and then perforated in the preferred fracture plane. Another sandstone block had a sliding sleeve valve cemented in place. Water was used to fracture these blocks and the fracture initiation pressures were measured. Good agreement between predictions and measurements was obtained, and the results indicated that high fracture initiation pressure is unlikely to be an issue with this completion method.

You can access this article if you purchase or spend a download.