Immiscible-Recycle Gas Injection to Enhance Recovery in an Iranian Naturally Fractured Reservoir: a Case Study with Emphasis on Uncertain Parameters

Abstract

Utiskivanje recikliranog plina je proces iskorištavanja ležišta od kojeg se mnogo očekuje u proizvodnji nafte i plina. Metoda koristi kontinuirano utiskivanje rentabilnog obroka proizvedenog plina kako bi se održala energija ležišta i iskoristila viskozna sila kao pokretačka sila. Postoje brojne studije o utiskivanju recikliranog plina u konvencionalna ležišta, međutim postoje neki drugi čimbenici kao što su lokacija bušotina i vrsta završnog opremanja, obrok i tlak utiskivanja, koji jako djeluju na konačni rezultat ove metode, a većini njih nije uzimana u obzir. U ovoj studiji je proučen proces utiskivanja nemiscibilnog recikliranog plina u jedno od iranskih prirodno raspucanih karbonatnih ležišta na opsegu polja. Stvarni model heterogenosti je konstruiran i simuliran pomoću Eclipse-100 modula (softver za simulaciju ležišta). Ispitani su učinci radnih parametara, kao što su broj i lokacija injekcionih/proizvodnih bušotina, proizvodnih/injekcionih obroka, vrsta opremanja i perforirani produktivni interval a rezultat je uspoređen s metodom prirodnog iskorištavanja ležišta. Utvrđeno je da je, osjetljivost obzirom na broj bušotina, 1 injekcijska/2 proizvodne bušotine najučinkovitiji slučaj. Kapacitet proizvodnje od 500 m3/d (3 145 bbl/d) i tlak na dnu bušotine od 25 bara (362,6 psi), dali su veću proizvodnju nafte. Završno opremanje injekcionih bušotina u frakturi i proizvodnih bušotina u matriksu, ima bolju proizvodnost naftnog polja u odnosu na druge slučajeve. Štoviše, uočeno je da je najučinkovitija vrsta završnog opremanja injekcionih bušotina vertikalno, a za proizvodne bušotine horizontalno. Rezultati su pokazali da je moguće postići značajno sekundarno pridobivanje korištenjem optimalnih uvjeta za utiskivanje nemiscibilnog recikliranog plina u to ležište.Recycle-gas injection is a promising recovery process to produce oil and gas. The method uses continues injection of the produced gas at economical rates to keep the reservoirs energy up and using viscous force as the driving force. There are numerous studies done on recycle-gas injection in conventional reservoirs, however, there are some other factors such as location of wells and completion type, rate and pressure of injection which highly affect the final result of this method and failed to be considered in the majority of them. In this study, we investigate the immiscible recycle gas injection process in one of the Iranian carbonate naturally fractured reservoirs on a field scale. The real heterogeneous model was constructed and simulated by Eclipse-100 module. The effects of operational parameters, such as number and location of injection/production wells, production/injection rate, completion type and interval, on the immiscible gas injection performance were investigated and the result were compared with natural depletion method. It was found that, in sensitivity with number of the wells, 1 injection/2 production wells was the most efficient case. Also well oil production rate of 3 145 bbl/d (500 m3/d) and well bottom-hole pressure of 25 bar provided higher oil recovery. Completing of the injection wells in fracture and production wells in matrix has a better field oil efficiency in comparison to the other cases. Moreover, it was observed that the most efficient type of well completion for injection well is vertical and for production wells are horizontal. The results revealed that the substantial secondary oil recovery can be achieved using optimum conditions for immiscible recycle gas injection in this reservoir