Breaking down the rock and initiating a fracture within pressure limitations is a major challenge in stimulating tight reservoirs with high tectonic stress components. Complexity increases with overbalanced mud damage and the stress cage created in the near-wellbore region during drilling. In certain formations, this results in 50% failed stages where proppant or acid were not placed. It is critical to investigate the first step in the process, which is the technique used to connect the wellbore with formation rock.
This paper presents an in-depth comparison of three primary techniques—conventional perforating, abrasive jetting with Coiled Tubing (CT), and circular notching with CT—through laboratory experiments, field cases, and, most importantly, intervention. Fracturing pressure reduction by circular notches and discrete perforation holes was compared in hydraulic fracturing laboratory experiments. These tests were conducted in a polyaxial load frame on 24×18×18 in. cement blocks, where wellbore features were precisely casted. In field case analysis, the three techniques were evaluated by comparing the injectivity index changes in offset wells in the same formations. The required intervention methods with CT and variable bottomhole assembly configurations are detailed and aligned with challenges associated with different completion types.
Hydraulic fracturing laboratory experiments were conducted at fixed confining stresses representing a general high breakdown pressure case of a horizontal openhole wellbore. The test series included the baseline case of nonintervened open hole parallel to the minimum stress, circular notch, and single and triple in-plane perforation holes. Notches and perforations were also tested in an azimuthally deviated horizontal well. Laboratory experiments confirmed the theoretically predicted superiority of notches over holes and demonstrated that notches can reduce fracture initiation pressure by up to 40%. For the field-scale evaluation, six comparison cases were built in similar reservoir and geologic conditions. A well injectivity index was calculated utilizing maximum pressures and rates achieved with different techniques. Injectivity enhancement showed up to 7X increase through abrasive jetting and circular notching over conventional perforating in casedhole and openhole wells, respectively, in wells that initially had injection. In some cases, these techniques enabled injectivity where initially there was no injection, hence yielding an infinite-scale enhancement. Finally, systematic intervention workflows were devised with different CT conveyance configurations and sequence for different completions such as abrasive jetting in cased hole, circular notching in open hole, and circular notching in open hole with packers and fracturing sleeves.
The paper presents a unique integrated comparison of three primary wellbore-rock connection techniques that will allow better engineered workflows to enhance stimulation and operational efficiency. These improved workflows will help increase production from tight assets and lower completion costs and associated emissions by reducing interventions.
