Water Shutoff in Fractured Carbonate Vertical and Horizontal Wells by Bullhead Chemical Injection: A Success Story

Abstract

Abstract Many wells in GCC (Gulf Cooperation Council) are producing from fractured carbonate reservoirs under aquifer or water injection pressure support. After water breakthrough, these wells suffer from high water cut production and low oil production caused by water channeling. An original technology using combination of microgel and gel was successfully implemented in an open hole fractured horizontal well under aquifer support (SPE 203394). This technology enables bullhead injection while minimizing the risk of damage. The treated well almost doubled oil production rate for one year along with a drop in the water cut from 92% to 80%. Three new campaigns of Water Shutoff treatments were performed in 2 years, using the same technology in the same type of reservoir. The treatment consisted of microgel injection, followed by gel, followed by microgel again. These sequences enable protecting the matrix from gelant leak-off and keeping open the fracture network surrounding the wellbore once the gel is in place. The total volume of treatment was around 250 m3. The size of the different slugs was adjusted according to well characteristics (open interval, flow rate, etc.). Diagnostic prior to the treatment using WOR Chan plots helped to identify the wells suffering from strong channeling. All chemicals were injected in bullhead mode. Most injections were performed through the annulus without pulling out of the hole the tubing string BP and ESP pump. Injection rate was between 1 and 3 BPM. Over the 11 wells submitted to the WSO treatments (two vertical and nine horizontal producers), four responded very positively, showing a sustainable additional oil production over time, five responded positively for several months, and three did not respond markedly. After treatment, for all the wells, the gross production could be maintained resulting in extra oil production along with water cut reduction. No well has been damaged by the treatment confirming the validity of the low-risk approach of this chemical injection strategy. After continuous surveillance of each treated well, from decline curves analysis and cumulative oil vs. cumulative water plots, the additional oil production is estimated as 165,000 bbl by end of Dec 2022, and keeps growing with time. This result has been obtained with mature wells that were producing with very high water cut (between 86 and 100%) before the treatment. The water shutoff technology combining microgel and gel can be applied in many reservoirs suffering from water channeling through fractures. This technology is low risk and can be used either in horizontal and vertical wells. Chemical injection proceeds rigless and bullhead, thus at low cost, and showed efficiency in very high water cut wells, inducing production of large quantity of additional oil in a mature field.