Alkaline Surfactant-Polymer Formulation Evaluation in Live Oil Conditions: The Impact of Temperature, Pressure and Gas on Oil Recovery Performance

Abstract

An Alkaline-Surfactant-Polymer / Surfactant-Polymer (ASP/SP) design study generally includes intensive work. Hundreds formulations have to be tested to screen phase behavior and typically a dozen of corefloods are performed to select the best formulation and further optimize the injection strategy/slugs design to match economic criteria.To be extrapolated to the field, it is critical to perform these tests in conditions as close as possible to real reservoir conditions: reservoir temperature, injection brine, reservoir pressure and reservoir oil. Specifically, dissolved gas and highpressure tend to significantly impact crude oil properties, and subsequently formulation behavior and performance, even when limited amount of gas is present. Ideally, this parameter should be considered from the beginning of the formulation design. However, considering the high number of tests to perform, as well as the relatively high cost and technical challenges associated with live oil experiments, it is unrealistic to routinely perform all the required experiments in high-pressure environment.We will present here the methodology developed to design surfactant based process by mimicking the impact of reservoir gas and pressure on the reservoir stock-tank oil. First a thermodynamic model based on an equation of state is fitted to reservoir PVT data (Gas/Oil Ratio or GOR, stocktank oil and associated gas composition analysis, bubble pressure and volumetric factor Bo) to predict consistent thermodynamic behavior and properties of the live oil. This step allows us to validate the reservoir conditions. A recombination of stock-tank oil with gas should be then performed to obtain the fluid in the reservoir conditions. Then we will illustrate through case studies how to combine a high-throughput robotic platform and a high-pressure/high-temperature cell to determine a representative crude oil matching live oil main properties, namely viscosity and Equivalent Alkane Carbon Number (EACN). This representative crude oil is obtained from the reservoir stock-tank oil which has been adjusted, using solvents or alkanes, to present the same characteristics as the reservoir live oil. This oil will therefore be used for an exhaustive formulation design and process optimization. Finally, we will compare oil recovery performances with the representative crude oil and with the reservoir live oil.

Status of surfactant EOR technology

“…The above phase behavior tests with "live oils" can be conducted using high-pressure and hightemperature sapphire tubes (Jang et al, 2014;Oukhemanou et al, 2014). Live oils can be dead oils dissolved with light components like methane at the reservoir pressure, or dead oils diluted with solvents based on the concept of equivalent alkane carbon number at the atmospheric pressure.…”

Equivalent Alkane Carbon Number of Live Crude Oil: A Predictive Model Based on Thermodynamics

“…In Equations (4)- (6), we assume that the dead crude oil can be represented by its EACN (EACNdo) determined experimentally as detailed in references [23,24]. The live crude oil EACN can be expressed as a function of EACNdo and gas EACN (EACNg) assuming a linear mixing rule based on volumetric fractions (Eq.…”

“…With our apparatus we can separately study the impact of the amount of gas dissolved in the live oil, and the impact of the pressure with pressures up to 500 bar. More details about experimental procedure and apparatus are provided in previous works [23,24]. This experimental procedure has been applied to crude oils #01 to #13 and so obtained results are presented in Table 2.…”

“…The determination of EACN for the dead crude oil (EACNdo) and the live crude oil (EACNlo) represents important steps during surfactant formulation design. For instance, EACNdo and EACNlo are key parameters for the determination of the Representative Crude Oil (RCO) -dead oil adjusted with solvents to mimic at lab scale, live oil characteristics at reservoir conditions - [24]. For EACNdo, it can be experimentally performed using test tubes and salinity scans, then matching phase behavior (WIII) of the {brine/formulation/dead crude oil} microemulsion with that of the most similar {brine/formulation/n-alkane} system.…”

“…Recently, Wan et al proposed a review and comparisons of existing approaches usable to experimentally determine the EACN of a dead crude oil [9]. The determination of EACNlo can be performed as described by Oukhemanou et al [24] but it necessitates time-consuming and hazardous High Pressure (HP) -High Temperature (HT) experiments. In order to reduce the number of such experiments during surfactant formulation, we propose hereafter the development and applications of a relation between EACNdo and EACNlo involving reservoir conditions such as temperature, pressure and the initial gas to oil ratio (R si ).…”