Subscriber access provided by READING UNIV
Article
Effect of oil presence on CO2 foam based mobility control in High Temperature High Salinity Carbonate Reservoirs Eric Sonny Mathew, Abdul Ravoof Shaik, Ali M. AlSumaiti, and Waleed S. AlAmeri Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03490 • Publication Date (Web): 02 Feb 2018 Downloaded from http://pubs.acs.org on February 5, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Effect of oil presence on CO2 foam based mobility control in High Temperature High Salinity Carbonate Reservoirs Eric Sonny Mathew1, Abdul Ravoof Shaik2, Ali Al Sumaiti3, Waleed AlAmeri4 ADNOC Research and Innovation Centre, Petroleum Institute, Khalifa University of Science and Technology, Abu Dhabi, UAE KEYWORDS Mobility control, Carbonate, HTHS, CO2 foam, Texture-implicit local equilibrium model, surfactant, CO2 gas, oil, Chemical EOR ABSTRACT Foam is one of the most cost effective means of solving the drawbacks associated with the process of gas injection. The presented work is focused on probing the impact of oil saturation on CO2 foam generation and its stability in the presence of high temperature and high salinity conditions. In this work, initially a texture-implicit local equilibrium model is used for parametric matching of a core flooding experiment conducted in the absence of oil. Once the foam parameters are calculated and tuned, the designed model is later up-scaled and studied with the inclusion of oil. The key objective is to study the effect of miscibility on the foam displacement front and the degenerating effect instilled by the residual oil saturation on the stability of foam. Different field scale models are designed and compared to validate the observed effect and hypothesis. The results of this work suggests that during CO2 foam flooding the oil saturation has profound effect on oil recovery especially when CO2 in immiscible state with oil when compared with miscible state. INTRODUCTION In the petroleum industry, it is a common practice to inject water into reservoirs to maintain the reservoir pressure. The literature suggests that about 65% of the hydrocarbons in place remain behind, in general, after natural drive and water flooding [1-3]. This is the juncture where Enhanced Oil Recovery (EOR) comes into play. Gas injection is a type of EOR technique which has been gaining popularity over the years in various geological formations. Despite its huge potential, this technique seems to give a much lower recovery than anticipated. For example, up to 20% of the original oil in place for CO2 in miscible condition [4, 5]. This poor performance of gas injection as an EOR method can be attributed to the numerous challenges it faces, the prominent of which is contributed by the low
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
density and viscosity of CO2 gas (when compared to that of oil and water) [6]. In addition, the high mobility of CO2 gas worsens the effect of gravity thereby forming high mobility channels, which ultimately lead to an early breakthrough of gas [6-8]. In order to negate or rather alleviate these setbacks, foam can used as one of the most promising and cost effective means of EOR [5]. Foam can be defined as a dispersion of gas in liquid such that the liquid phase is interconnected and at least some of the gas flow paths are blocked by lamellae [9]. Foam reduces mobility of gas by trapping the gas bubbles in porous media and presence of these bubbles provide stability to the displacement process by increasing the gas effective viscosity [3, 10-12]. Further foam possesses a unique ability to block high permeable layers (layers already swept by gas) thereby leading the injected fluid to layers and regions that were previously un-swept. This property of foam proves to be highly advantageous in heterogeneous reservoirs [13]. The foam strength is attributed to the value of apparent viscosity of foam and the observed trend is that it increases with increase in foam quality in the low quality regime and then reaches a maximum, beyond which the increase in foam quality leads to a decrease in apparent foam viscosity in the high quality regime [14, 15]. The mentioned apparent foam viscosity is represented mathematically as =
∆ .
where, k – core permeability, u – total superficial velocity, ∆P – pressure drop, L – core length. It can be said without doubt that a higher apparent viscosity indicates stronger foam. Foam can be classified into two main types: continuous and discontinuous gas foams. In the case of continuous foam, the gas has to go a longer way to move through the porous rock but still has an open pathway to flow through the foam. Hence only the mobility of gas (relative permeability of gas) is affected [13]. On the contrary, discontinuous gas foam restricts the gas to flow through the foam as all the flow paths are blocked by the lamellae formed [9]. Thereby, the gas needs to exceed the differential pressure displacing the lamellae in front of it, in order to flow through the porous media [13]. Hence, this phenomenon not only affects the relative permeability of the gas but also contributes in giving the CO2 gas an apparent viscosity value that is higher than its original value. The flow resistance of the lamellae is responsible for the high value of viscosity [13] . The aforementioned categories are depicted in Fig. 1.
ACS Paragon Plus Environment
Page 2 of 25
Page 3 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Fig. 1- Illustration of continuous and discontinuous gas foam [16]
EFFECT OF OIL ON FOAM STABILITY The efficiency of foam as an effective displacement process depends highly on its stability in reservoir conditions. Some of the factors affecting foam’s stability are surfactant concentration, oil saturation, oil mole fraction, salinity, shear thinning, and a multitude of several others. Among these, one of the major hindrances to the establishment of foam as a successful EOR process is the adverse influence of oil on its stability as well as the complex interaction between both of them [12, 17]. It is a well-known fact that crude oil is made up of different types of hydrocarbons, a percentage of Oxygen, Sulphur, Nitrogen, and also various metals in which the hydrocarbons comprises of varying amounts of paraffin, aromatics and naphtene. This complex composition contributes to different physical and chemical properties [18, 19]. Typically oil has the ability to remain as a continuous oil phase in the liquid films or be solubilized in the micelles or even remain as an emulsion. Hence, it is significant to point out that the behavior of oil and its properties are crucial in determining whether oil will or will not influence the stability of foam [18]. The four main theories proposed in the literature which investigates the effect of oil on foam stability are spreading and entering coefficients, lamella number, bridging coefficient, pseudoemulsion film theory [18]. a) Spreading and entering coefficients: Literature suggests that two parameters that determine the stability of foam in the presence of oil is closely related to a negative Entering coefficient denoted as E which implies that a Spreading coefficient denoted as S should be negative as well[20-23]. The aforementioned parameters are calculated using interfacial and surface tensions as denoted below, = ⁄ ⁄ ⁄
(1)
= ⁄ ⁄ ⁄
(2)
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
where, ⁄ represents the surface tension between water and gas while the surface tension between water and oil is denoted by ⁄ . Finally the surface tension between oil and gas is given by ⁄ [18]. In principle, if the spreading coefficient S is a positive value then it implies that oil will spread at the surface and break the foam. On the other hand as mentioned earlier, if the value of S is negative then the oil will remain as a droplet at the surface which is the condition necessary for the foam to remain stable and undeterred [18]. The mentioned scenarios are depicted in Fig. 2. Furthermore, the spreading coefficient cannot be a positive value at equilibrium [24]. Oil
Foam
(a) (b) Fig. 2 - (a) S0, spreading system [18] b) Lamella Number: The tendency of an oil phase to become emulsified and imbibed into a foam lamella is represented by lamella number ‘L’ which is given by the below equation [25]: = 0.15
⁄
⁄!
(3)
Based on the value of L, foam can be distinguished to three different types as A, B, and C [25, 26]. If the lamella number, L
