Comparison of Matrix Acidizing, Acid Fracturing and Proppant Fracturing for Stimulation of a Carbonate Exploration Prospect in Pakistan

Abstract A gas bearing Paleocene to Early Eocene carbonate formation is present in a fold and thrust belt in Pakistan and is a current exploration target. This formation overlies a Cretaceous clastic\sandstone formation, which is currently being produced from many wells, providing logging data indicating its thickness over a wide area. The carbonate formation consists of both massive and thin\thick bedded limestones and marlstones. Available data indicates that porosity and permeability are extremely low, and although natural fractures are likely present, their properties are unknown. A study was conducted to predict the potential benefits of three stimulation methods—matrix acidizing, acid fracturing, and proppant fracturing—to determine if any of these methods could lead to the creation of an economic well. Core from a recently drilled well was subjected to a suite of regular and special core analyses to assist in evaluating the formation properties and providing data for stimulation design. A prospective location has been identified in a neighboring field where the carbonate formation is known to be significantly thicker, presenting a more attractive target for an appraisal well. A study was performed using industry-standard simulation tools to determine what kind of stimulation effect (negative skin or effective fracture half-length and conductivity) could be achieved. These results were entered into a single-well, single-layer, single phase reservoir simulation model to obtain production forecasts, which were then compared with a base-case unstimulated vertical well. The study results indicate that based on the currently available data, the potential for matrix acidizing is not sufficient to make an economic well. Acid fracturing is a potential strategy, although significant uncertainties remain regarding the long-term behavior of an acid fracture in this type of formation. Propped fracturing delivers the largest stimulation benefit with the least uncertainty about the long-term performance but carries significant placement risks based on experience in the underlying sandstone formation. This work presents an investigation into a new potential gas-producing formation in Pakistan based on log and core data, and it compares the potential benefits of three different stimulation methods. The results of this study are beneficial for other operators who are considering exploration or appraisal wells in this carbonate formation or other similar unconventional targets.