Application of Multistage Acid Fracturing to Stimulate Mishref Carbonate Formation: Case Study, Minagish Field, West Kuwait

Abstract

In recent years, field development strategies have begun to prioritize horizontal well technology over vertical and deviated wells because of the advantages of maximized reservoir contact, higher production rates, and better access to available hydrocarbon reserves. Some of the horizontal wells completed with openhole wellbores in carbonate formations are actually stable and good producers when the reservoir permeability is sufficiently high to not require a large or complicated stimulation treatment. If the permeability is low (i.e., less than 10 mD), as in most cases, this type of completion challenges any type of acid stimulation because of the well architecture and resulting poor distribution of the stimulation fluid over the entire lateral section. The Mishref reservoir of the Minagish field, located in western Kuwait, is a tight carbonate formation with poor reservoir quality and relatively low reservoir pressure; it was completed conventionally with openhole wellbores. The acid stimulation treatments performed in this area that showed positive results led to the selection of a multistage acid fracture stimulation of shorter horizontal wells. To enhance production in this field, the lateral length of the horizontal wells has been increased; the increased length, however, has also increased the challenges associated with proper stimulations if these issues are not considered during the completion stages of the wells. To maximize and sustain hydrocarbon production in long horizontal open holes, a multistage acid fracturing stimulation is still required if selective tools are used to complete the openhole section. The selective completion tools enable the mechanical segmentation of the annular space of the wellbore by dividing it into the required small isolated intervals based on petrophysical and reservoir properties. The isolated sections can be selectively stimulated to maximize the productivity in one continuous intervention. This paper summarizes the design processes, stimulation challenges, production response, and lessons learned from one multistage acid fracturing stimulation performed on a well drilled and completed in the Mishref reservoir of the Minagish field. In this well, the entire 1,800-ft length of the openhole lateral was divided into seven isolated stages by using swell packers and sliding sleeves. Because of the architecture and nature of the wellbore and the requirement to generate long fractures to properly drain the reservoir, the isolated compartment length (distance from the swell packers isolating the stage) was reduced to an average of 106 ft, and a sliding sleeve was placed in the middle of isolated sections. The paper documents the pilot multistage acid fracturing treatment on this type of completion; it also demonstrates the success of the stimulation in that the outcome exceeds the expected production increase, resulting in a more sustained production, as compared with the offset wells.