Batı Raman petrol sahasına CO2-köpük yönteminin uygulanabilirliği üzerine deneysel araştırmalar
Laboratory investigations on the applicability of CO2-foam method to Batı Raman oil field
- Tez No: 14133
- Danışmanlar: PROF.DR. AYTİN GÖKTEKİN
- Tez Türü: Doktora
- Konular: Petrol ve Doğal Gaz Mühendisliği, Petroleum and Natural Gas Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1990
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 117
Özet
ÖZET Türkiye'nin en büyük petrol sahası Batı Raman'da üretimi artırmak için karışamaz bir C02 enjeksiyonu yapılmaktadır. İlk saha sonuçlarına göre petrol üretimininde önemli artışlar sağlanmıştır. Bununla birlikte, rezervuarın çatlaklı yapısı ve ağır petrol içermesi nedeniyle, CO 'nin üretim kuyularına giderek artan oranlarda gelmesi bir sorun olarak ortaya çıkmıştır. Bu sorunu azaltarak, öteleme verimini artırmak için köpükle ötelemenin yapılabileceği belirlenmiş ve bu yöntemin uygulanabilirliğini araştırmak üzere deneysel bir çalışma yapılmıştır. Batı Raman rezervuar koşullarında performansını uzun süre kaybetmeyerek gaz mobilitesini düşürecek nitelikte köpük üretebilecek yüzey aktifleyicileri seçmek için ilk olarak statik köpük deneyleri yapılmıştır. Bunun sonunda, kullanılan 20 adet yüzey aktifleyiciden yalnız üçünün Batı Raman formasyon suyu tuzluluğunda uygun köpük oluşturulabildikleri görülmüştür. Bunlarla birlikte, tuzluluktan az etkilenen üç yüzey aktifleyici daha sonraki deneylerde kullanılmıştır. Statik deneylerde C0_ ile oluşturulan köpüklerin stabilitelerinin yüksek basınçta (5.8 MPa), atmosfer basıncındakinden daha yüksek olduğu ve stabilite açısından optimum bir yüzey aktifleyici madde konsantrasyonunun varlığı belirlenmiştir. Yüzey aktifleyicilerin rezervuarda tutulmalarının incelendiği deneylerde Batı Raman petrolünün düşük konsantrasyonlarda (% 0.1-0.2) yüzey aktifleyicilerin yarıya yakın kısmını bağlayabildiği görülmüştür. Batı Raman karotlarında yapılan deneylerde adsorbsiyona bağlı tutulmanın 0.15 - 0.25 mg/g olduğu belirlenmiştir. pH, akış hızı ve kayaç yapısındaki değişimlerin adsorbsiyona etkisi statik ve dinamik deneylerle incelenmiştir. Statik deneylerde iyi sonuç veren yüzey aktifleyi- cilerin gözenekli ortamdaki performansları kumtaşı ve Batı Raman (kalker) karotlarında yapılan dinamik deney lerle araştırılmıştır. Köpük oluşumunun gaz mobilitesi ni kumtaşı karotlarda 6-7 kat, Batı Raman karotla rında ise 4-5 kat düşürdüğü saptanmıştır. Yüzey ak tifleyici madde konsantrasyonu, akış hızı, sıcaklık ve petrolün köpük oluşumu ve performansına etkisi de bu deneylerde belirlenmiştir. Batı Raman Rezervuarının çatlaklı yapısı dikkate alınarak, çatlatılmış karotlarda da dinamik deneyler yapılmış ve sonuçları tartışılmıştır. -xı-
Özet (Çeviri)
SUMMARY LABORATORY INVESTIGATIONS ON THE APPLICABILITY OF C02-FOAM METHOD TO BATI RAMAN OIL FIELD In Batı Raman field, containing the largest oil reserves in Turkey, an immiscible C0~ displacement is in progress. In a fractured and heterogenous reservoir, Batı- Raman has heavy oil reserves. These rock and fluid properties are causing an early breakthrough of C0“ during the injection; therefore reducing the performance of the displacement. As the oil in the fractures is saturated with C0_, the oil production increases. However, once the substantial part of the oil in the fractures has been produced, the production decreases to a level where the only production mechanism is due to the diffusion of C0”into the oil in the rock matrix. A“literature survey of enhanced oil recovery (EOR) methods shows that foam by reducing the mobility of the gas in the fractures, thereby blocking gas, is a promising method of EOR for increasing the performance of C0_ displacement in Batı Raman field. This study is an experimental research of the applicabi lity of CO_-foam method to Batı Raman field. In foam displacement, first a foaming solution is injected into the reservoir and, later, displaced by a gas. This solution is a brine containing surface active agents (surfactant). For a succesful foam displacement, a surfactant able to generate enough and stable foam is needed. To achive such, its concentration in the solution should not fall below a certain limit as a result of loss in the reservoir. The theories are yet to be developed to help select the most suitable surface active agent to generate a good foam with minimum concentration under reservoir conditions. Therefore, surface active agent selection requires a laboratory research, and there exist some experimental procedures of such a selection. In this research, the foamability of 20 surface active agents manifactured by various companies were tested under simulated Batı Raman reservoir conditions. The retention properties and the porous media flow performance of the surface active agents that gave better results at the preliminary tests were determined, The conclusions are summarised below: -xii-Static Foam Experiments: In these experiments, under atmospheric conditions, a gas was passed through a glass tube, and the maximum volume, and the half life of the foams were determined. It was found that the salinity of Batı Raman formation greatly reduces the foamability of most of the surface active agents. Three surface active agent solutions (CD-128, PAI and S-50) in brine showed foamability properties that are almost equal to their foamability in fresh water. They are all ethoxylated anionics surfactants known as modified surface active agents. Later, three more surface active agents (O-SAP, N-40, C-10) that had been slightly affected by salinity were also included in further experiments. Critical miscelle concentration of these surface active agents were determined by measuring their surface tension. Foam stability is adversely affected by high electrolyte content since the lamellea electrostatic double -layer thickness is reduced. In the static experiments, foams generated with C0”were less stable than the ones generated with air, and the reason for this is.the increasing diffusion of gas in lamelles because of high solubility of C0“ in water. An increase in gas diffusion accelerates the transportation of gas from smaller bubbles, and this continues until bubbles disappear. To investigate foamability of the selected surface active agents under reservoir conditions, static high pressure (5.8 MPa) experiments were conducted. Two important results were concluded from the experiments; first, increase in stability of foams with increasing pressure and the second the presence of an optimum surfactant concentration for which the stability shows a maximum. The foam stability increases at high pressure is considered to be a result of decreasing rate of the solubility of C0”in water. The effect of concentration on foam stability can be explained by Gibbs-Marangoni pheonomenon. When foam is generated, the surface tension on film surface is reduced and a surface tension gradient along the film is created. If the surface active agent concentration in the bulk fluid in the film is sufficienty high, the surface active monomers tend to bring immediately the surface tension to its previous state. The prevention of Gibbs-Marangoni phenomenon, the balancing of surface tension gradient with movement of fluid developed along the film surfaces, reduces foam stability. In aging tests where surface active agents are held under reservoir conditions for one month, a reduction of pH and surface active agent concentration (up to 15%) -xiii-were observed. However, no significant changes were noticed in foamability of these solutions. Retention Experiment: During the high pressure experiments with PAI and CD-128, it was observed that about 22 % of the surfac tants were deactivated by Batı Raman oil at high concentration ( 0.35 % vol.). This demonstrates that deactivation would be the most important retention mechanism. The adsorption of anionic based surface active agents were determined with batch-type static and dynamic experiments. The adsorption of the modified surface active agents on Batı Raman cores was 0.15-0.25 mg/g. The least absorbed agent was PAI and its plateau value for brine solutions was 0.15 mg/g. The absorption of the other non-ethoxylated surface active agent (N-40, 0- SAP) in brines was found to be very high (0.50-0.60 rag/g) probably due to precipitation. The effects of pH, gas velocity, and core structure on absorption were also investigated with static and“dynamic experiments. When pH is around 3, it was found that the absorption on crushed limestone increases about 2-2.5 times. The velocity also affects the absorption. At low velocities, increasing residence time of surface active agents, increases the absorption. In experiments with low permeability frac tured cores ( 3-5 md) to simulate the fractured Batı Raman reservoir rock, the absorption was observed to be very low since the effective surface area wetted by the fluid is decreased. Dynamic Experiments: The behaviour of the foams generated in porous media with the solutions of surfactants selected after static experiments, were investigated with dynamic experiments. With this objective in mind, an experimental apparatus sensitive to the solutions, gas and oil, and the core sample was used. The pressures at the inlet and outlet of the core were continiously recorded. In experiments with and without oil, the effect of various factors on gas mobility were determined with the ratio of the pressure difference that determines the generation of foam to the pressure difference (loss) while water is displaced by gas under same conditions. This ratio is named mobility factor. In these experiments, sandstone and Batı Raman core samples were used. The sandstone cores have a permeability of 3000 ± 100 md and a porosi ty of 0.22-0.23. The permeability and porosity of Batı Raman core were 54 md and 0.23 succesively. -xiv-The summary of the experiments run on these cores is given below. Effect of Salinity: Effect of salinity was more dominant for non- ethoxylated surface active agents. O-SAP, an anionic surfactant, caused an abnormal pressure behaviour, probably indicative of precipitation. The performances of CD-128, PAI and S-50 were not affected by the salinity while a decrease by a factor of 6-7 in gas mobility was observed. Effect of Concentration: The effectiveness of the solutions in porous media reaches a maximum in concentrations just above the critical miscille concentration, and further increases in concentrations beyond this level do not increase effectiveness. Effect of Temperature: In dynamic experiments, the temperature has an important effect in generation of foam. The experiments were conducted at Batı Raman reservoir temperature, 65 °C. It was found that this was the ideal temperature for surface active agents used in this study. There are considerable differences between the experiment results at 65 °C and 20 °C. At 20 °C, while the fluid caused a decrease in gas mobility by a factor of 2-3, same factor reaches 6-7 at 65 °C Effect of (Gas) Velocity: A velocity of 7.2 m/day was used in these experiments. The experiments at three other gas velocities were also conducted. It is found that the foam generation is decreased with increasing fluid velocity and, accordingly, the gas mobility is increased. Effect of Gas: No changes in performance of the surfactants were observed when air is used as gas phase instead of co2. Effect of Oil: In experiments run with Batı Raman oil, no signi ficant effect of oil on foam generation in porous media was observed. Bata Raman oil's spreading coefficient determined by surface tension measurement is -28 mN/m. -xv-This shows that Batı Raman oil is not going to be spread on the foam surface and; thus, foam stability will remain unaffected. On Batı Raman core samples, dynamic experiments were conducted with the solutions of PAI and CD-128 In these experiments foam generation caused a decrease by a factor of 4-5 in gas mobility. These mobility factor values are less than those obtained in sandstone experiments. In the literature, there are also some data indicating the role of permeability on foam performance in porous media. The gas blocking effect of the foam is found to be higher in more permeable cores. This phenomena is relied on two important factor. The first is the texture of the foam. It is determined that foam flows as a bulk foam or as a lamellea filling the pore space depending on the radius of pore channel and the foam viscosity increases with increasing pore channel radius. The second is the magnitude of capillary inlet pressure; in low permeability cores this pressure could be higher than the limiting capillary pressure necessary for the formation of a stable foam. In experiments run with Batı Raman oil, it was found that in-situ foam generation could have a very important effect on C0”displacement. In the experiments conducted using 0.5% PAI solution, the oil saturation was reduced from 0.64 ± 0.01 to 0.57 ± 0.01. The increase of gas saturation in the core with foam formation could have a positive effect on C0“ application considering the importance of increasing gas saturation on the diffusion of C0”into the matrix. To better simulate the fractured structure of Batı Raman reservoir rock, core samples with low initial permeability (3-5 md) were artificially fractured. The fractured core permeabilities were measured to be between 350-1500 md depending on the applied overburden pressures. The experiments were conducted using 0.5 % solution of PAI in brine. Generation of foam in fractures was found to be a function of fracture height. Reduction in mobility (MF=2.5) was high at low permeabilities, and decreased with increasing permeability. However, these results were believed to be inconclusive, therefore the experiments should be repeated with models that can better simulate the heterogenous structure of Batı Raman reservoir. -xvi-
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