Addressing the Near-Wellbore Injectivity Limitations while Fracturing Highly Pressurized Formations

Abstract

Fracturing in tight and deep gas formations can be challenging when near-wellbore stresses reduce injectivity. The drilling fluid may contribute to a near-wellbore damage, and this will exaggerate the rock breakdown limits additional to the high local stresses. Study was dedicated to understanding the main contributing factors and suggest the comprehensive workflow to minimize occurrence and non-productive time (NPT) associated with abovementioned challenges. Statistical analyses over several years and hundreds fracturing stages were taken as a basis for the study. Wells were divided into several groups including orientation, completion and formation type criteria. Injectivity test was consistently performed prior to the main fracturing operation and was used as a main tool to forecast the severity of the near-wellbore issues. Based on the pressure response during and immediately after the test it was possible to build a decision tree for the next step in fracturing operations. Engineering workflow was further calibrated in the real-field case studies. Results of the study revealed that the most challenging completion scenario in respect to near-wellbore injectivity challenges was a horizontal cemented liner with plug and perf technique. In carbonate formations, up to 30% of the stages experienced injectivity limitation of various severity in several group of wells. Acid squeeze was identified as most reliable an operationally affordable method for carbonate formations. Another effective solution, applicable to clastic rocks too can be a degradable particulate for the abrasive perforation that improves injectivity and leaves a clean wellbore without need for cleanout. Interestingly, largest likelihood of the near wellbore block occurred in the very first stages (toe sections) of the horizontal wellbores and reached up to 50% rate in some categories. Coiled tubing -conveyed perforation and cemented multistage fracturing completions were implemented to servce as a solution to minimize inefficiencies and NPT as well as risks associated with conventional operations utilizing tractors in horizontal wellbores. Implementation of decision tree derived as a result of the study allowed reducing NPT of operator and service company. Considering large number of equipment and personnel involved in such integrated completion and fracturing projects it represents significant value for both quality and HSE aspect and increase efficiency of the operations which is of primary importance when developing tight reservoirs. Study provides large statistical summary and up-to-date practices of deep and tight rocks fracturing and solution from several regions.