Abstract
The paper summarizes field results and data which indicate the effectiveness of open hole packers vs. cement in providing competent hydraulic isolation of well segments in horizontal multi-stage completions. The application of multistage fracturing treatments to horizontal wellbores has facilitated unparalleled reservoir access, which is the catalyst for tight-rock exploitation. Whether created utilizing a cemented wellbore or an open-hole (O/H) packer style of completion, the massive surface area of induced and dilated fractures is a key ingredient for the successful completion of low permeability formations. Unfortunately, many of the commonly used completion systems offer little or no indication of the effectiveness of the hydraulic isolation between fracturing stages. In completions employing ball-activated sleeves in combination with O/H liner packers, the only indication of failed hydraulic isolation is masked in the surface treating pressure data collected during the frac. Multiple stages in the tubing at the same time can have the effect of masking the treating pressures as friction and increased hydrostatic pressure of the sand slurry have competing effects. This difficulty in interpreting the surface pressure readings can result in segments of the wellbore being either bypassed or overtreated as a result of the fracture treatments coalescing, potentially preventing the recovery of the targeted reserves. The paper reviews and compares data collected through the application of a combination of Coiled Tubing Unit (CTU) operated frac sleeves with either O/H packers or cemented liners. The use of CTU in the isolation of individual frac stages offers the capability to collect downhole pressure and temperature data of each frac treatment at the frac port, which is typically not available through other methods. Because this data is collected downhole, it can provide clear indications of O/H packer or cement effectiveness in isolating discreet fracture stages, potentially identifying segments of the reservoir which may remain un-stimulated, or possibly over-treated. The downhole data collected through the application of CTU operated frac sleeves may be valuable for operators seeking to maximize the effectiveness of their stimulation programs through optimal packer placement or cementing design, and may potentially help to maximize EUR for multistage completions.
