Special features of fracture network in Iranian fractured reservoirs

Abstract

U raspucanim ležištima nafte zbog postojanja dva različita tipa porozne sredine, nazvane blokovi matriksa i pukotine, postoji više vrsti ponašanja ležišta. Zbog kompleksnosti strukture raspucanih ležišta, pridobivanje nafte je rezultat kombinacija nekoliko mehanizama proizvodnje kao što su gravitacijsko dreniranje i apsorpcija. Kapilarne i gravitacijske sile su dvije glavne sile koje kontroliraju ove mehanizme proizvodnje. Ovaj rad je usredotočen na utjecaj kapilarnog tlaka pukotina koji je različit od nule, relativnu propusnost pora koje nisu pravocrtne, pojavu reinfiltracije, visinu bloka matriksa i ponašanje aktivnih mehanizama u raspucanim ležištima za vrijeme prirodnog iscrpljivanja ležišta i injektiranja nemješljivog plina. Terenske studije simulacije polja napravljene su korištenjem simulatora ECLIPSE s formulacijom obične sirove nafte i opcijom dvostruke poroznosti. Rezultati simulatora, obzirom na relativnu propusnost pora koje nisu pravocrtne, pokazuju da utjecaj tog parametra na ponašanje ležišta ovisi ne samo o fizičkim svojstvima pukotina već i o kapilarnom tlaku praga matriksa i visini bloka matriksa. Rezultati simulacije pokazuju da je na pridobivanje nafte utjecao, u rasponu od 1% do 2%, razmatrani kapilarni tlak praga matriksa od 0,007 bara (0,1 psi) do 0,214 bara (3,1 psi). Isto tako na pridobivanje nafte utječe, u rasponu od 1,5% do 0,5%, razmatrana visina bloka matriksa od 4,57 m (15 f5) do 18,29 m (60 ft). Naši rezultati simulacije sugeriraju da je za raspucana ležišta s malom visinom bloka ili velikim kapilarnim tlakom praga matriksa, neophodno iznaći adekvatnu, od nule različitu, krivulju kapilarnog tlaka pukotina. Nakon toga smo proučili djelovanje relativne propusnosti zakrivljenih pora na ponašanje ležišta. Rezultati su istaknuli ovisnost utjecaja relativne propusnosti nelinearnih pukotina na visinu bloka matriksa. Rezultati simulacije dobiveni primjenom različitih visina bloka matriksa pokazuju povećanje iscrpka u rasponu od 2,3% do 5,2%, primjenom injektiranja nemješljivog plina. Stoga su ovi rezultati pokazali da ležišta s najvišim blokom matriksa mogu biti dobri kandidati za primjenu injektiranja nemješljivog plina.Due to the presence of two different types of porous media, namely matrix blocks and fractures; there are varieties of reservoir performance behaviors in fractured oil reservoirs. Because of this complex structure of fractured reservoirs, oil recovery is the result of the combination of several production mechanisms such as gravity drainage and imbibition. Two main forces controlling these production mechanisms are capillary and gravity forces. This work is focused on the influence of non-zero fracture capillary pressure, non-straight line fracture relative permeability, reinfiltration phenomenon and matrix block height on the performance of active mechanisms in fractured reservoirs during natural depletion and immiscible gas injection project. The field simulation studies were performed using ECLIPSE commercial simulator with black oil formulation and dual porosity option. Simulator results considering non-zero fracture capillary pressure indicated that the influence of this parameter on reservoir performance depended not only on fracture physical properties, but also it depended on matrix threshold capillary pressure and matrix block height. Simulation results indicated that oil recovery was affected by the range from 1% to 2% considering matrix threshold capillary pressure of 0.1 psi (0.007 bar) to 3.1 psi (0.214 bar). Also oil recovery was affected by the range from 1.5% to 0.5% considering matrix block heights of 15 ft (4.57 m) to 60 ft (18.29 m). Our simulation results suggest that for the fractured reservoirs with small block heights or with large matrix threshold capillary pressure, the appropriate non-zero fracture capillary pressure curve is necessary. Subsequently we have investigated the effect of non-straight line fracture relative permeability on reservoir performance. The results emphasized that the matrix block height depended on the influence of linear line fracture relative permeability. Simulation results acquired by applying different matrix block heights indicated the enhancement in oil recovery by immiscible gas injection in the range from 2.3% to 5.2% considering matrix block heights of 15 ft (4.57 m) to 60 ft (18.29 m). Hence, these results showed that the fractured reservoirs with the highest matrix block heights could be good candidates for implementing the immiscible gas injection operation