As development of shales and other tight formations has evolved, it has become clear that the key to optimum reservoir drainage is systematic well placement and an efficient fracture network that delivers maximum connectivity to the reservoir. That typically means the greatest number of wells and stages per well as is practical for a given acreage, without risking communication either between stages or between wells.
The most efficient fracture network, however, requires consistent stage spacing and uniform fracture volume, neither of which has been achievable using plug-and-perforate (PnP), the most common multistage completion technology. The limitations of PnP are well known and documented. Because the technique relies on stimulating multiple perforation clusters simultaneously, and because breakdown pressures vary widely across any lateral stage section, there is no control over which clusters actually fracture. Studies using radioactive tracers and production logs have revealed that a third or more of all clusters are not stimulated at all, while others receive varying amounts of treatment. That leaves only a few clusters to account for almost all of the proppant placed, indicating uncontrolled fracture volume as well as unpredictable placement.
When multiple adjacent and parallel wellbores are completed using PnP, the effects of the random fracture pattern are multiplied, with large areas of the formation unreached by the stimulation. One operator developing the Permian Bone Springs sandstone estimated that as much as 60% of producible reserves were stranded as a result of incomplete reservoir stimulation using PnP.
This paper compares those PnP completions with a subsequent completion using full-drift, cemented casing sleeves and a coiled-tubing-deployed frac-isolation assembly to achieve exact fracture location and uniform fracture volumes, regardless of varying formation breakdown pressures. This well was on the same lease property and was drilled in the same manner as those completed with PnP. The operator typically runs 44 evenly spaced full-drift casing sleeves in the completion string instead of 48 perforation clusters in 12 stages.
Throughout the stimulation operations, the operator was able to confirm the volume of proppant placed at every stage. This paper describes how the comparison wells were drilled and completed and presents production data that indicates a much more efficient fracture network across the entire lateral using the cemented casing sleeves. The paper also compares the operating advantages and disadvantages of the two completion methods.