Thief zone identification and classification in unconsolidated sandstone reservoirs: A field case study

Abstract

Channeling between injectors and producers leads to bypassed oil left in the reservoir, which is one of most common reasons that wells in mature oil fields experience high water cut after long-term waterflooding. Identification and evaluation of the higher permeable channels (thief zones) are the key to effectively plug these thief zones and improve the conformance of water flood. This study applies three different methods to identify and evaluate the thief zones of a water injection project in North Buzazi Oilfield, a thick-bedded unconsolidated sandstone heavy oil reservoir in Manghestau, Kazakhstan. The thief zones, which evolve as a result of formation erosion and sand production, are identified and classified with respect to four different levels of significance using fuzzy comprehensive evaluation, production/injection profile method and pressure index (PI) methods. Good consistency is observed among the identification results using these methods. Finally, we present two ways to quantitatively evaluate the characteristics of the thief zones using water–oil-ratio as the input, which can be readily applied for future field development design.

Identification of Gas Channeling and Construction of a Gel-Enhanced Foam Plugging System for Oxygen-Reduced Air Flooding in the Changqing Oilfield

“…Generally, the standard value of the comprehensive evaluation coefficient of 0.50 is selected as the limit for judging whether the channeling channel is developed [ 20 ]. For ascending the half trapezoid model, the larger the comprehensive evaluation coefficient value, the greater the possibility of the channeling channels existing in the oil reservoir around the injection and the production well groups during the oilfield development process.…”

“…Xu et al (2021) recognized and classified the channeling channels for the North Buzazi heavy oil reservoir using the fuzzy comprehensive evaluation, the production-injection profile, and the PI method. The identification results have good consistency among the three methods [ 20 ].…”