Description
ABSTRACT
World energy demand is increasing by industrial and life developments. Nowadays, fossil fuels, especially oil and gas, play a major role in providing energy compared to other methods of energy production such as solar, windy, etc. To supply the world energy demand, it is necessary to increase the petroleum reserves and production capability. Oil and gas production increase can be achieved by developing mature reservoirs or discovering new reservoirs. Differential pressure between reservoir and production well pulls the oil toward the production well and it is called as primary recovery. After this stage, gas or water is injected into the reservoir to maintain reservoir pressure. This stage is referred to as secondary recovery.
Enhanced Oil Recovery (EOR) techniques are employed to recover more oil from mature reservoirs after the primary and secondary oil production stages. Polymer flooding as a chemical EOR method involves adding polymer molecules in order to increase water viscosity. This study analyzes the rheological properties of polymer under various shear rate, polymer concentration and molecular weight, temperature, salinity and divalent for potential Enhanced Oil Recovery (EOR) application. Guar is the major polymer used in this study
CHAPTER ONE
1.0 INTRODUCTION
1.2 BACKGROUND OF THS TUDY
The Enhanced Oil Recovery (EOR) techniques are employed to recover more oil from mature reservoirs after the primary and secondary oil production stages. Polymer flooding as a chemical EOR method involves adding polymer molecules in order to increase water viscosity. The Enhanced Oil Recovery (EOR) process using polymer methods have been employed for the past 20 to 30 years ago in order to obtain maximum recoverable oil. There are many benefits of using polymers; they can increase the viscosity of water solution, enhance sweep efficiency and also reduce mobility ratio between water and oil (Niu et al., 2001). According to Achim et al. (2015), gelled polymer technology could be applied to seal high permeability zones and fractures, resulting in improving sweep efficiency and oil recovery. PETRONAS found that polymer flooding can be justified economically and environmentally because polymers are non-toxic and do not cause serious environmental problems (Caenn et al., 1989). It is simple and has a relatively low operating cost compared to other EOR methods. This EOR process could be monitored using a real-time approach of streaming potential measurement using electrodes permanently installed downhole (Mohd et al., 2017b), which is potential to monitor alkaline-surfactant-polymer (ASP) flooding (Mohd et al., 2017a). Besides its potential application in EOR, polymer provides a significant contribution to polymer electrolytes, which is a mixture of organic polymer and inorganic salt. This study includes the use of polymer based electrolytes such as cellulose acetate (Abidin et al., 2014) and poly(ethylene oxide) (Chan and Kammer, 2014) on impedance spectroscopy (Chan and Kammer, 2016). It is the usual practice to select polymer based on its rheological characterization and its effect on oil recovery (Zheng et al., 2011). As polymer passes through the reservoir, there is a change in its physical and chemical properties due to formation absorption, shearing and chemical reactions. Generally, there are two commonly used polymers in EOR applications which are those produced synthetically and those that are natural products of wood and seed or those produced by bacteria or fungi. All of these polymers have their rheological properties compromised by the conditions found in the reservoirs such as high temperature, high salinity, the presence of malignant bacteria, and the hardness of connate water (Mothe et al., 2006). Different rheological regimes have been discovered when polymers with elastic properties are injected into a porous medium (Zhang et al., 2011). Shear thickening and thinning occurs at high and low fluid velocities in porous media, respectively. Further increase of velocity could result in polymer degradation due to rupture of the polymer chain (Al Hashmi et al., 2013). In EOR applications, polymer must be stable at reservoir condition for an expected residence time in the reservoir rock as it can degrade under certain conditions. As the rheological properties of polymer depend on several parameters, this work therefore analyzes the rheological properties of polymer under various shear rate, polymer concentration and molecular weight, temperature, salinity and divalent. Such an approach would help the study to select the most potentially suitable polymer for potential EOR application.
The polymer flooding has several benefits including improving mobility of injected fluid, increasing vertical and areal sweep efficiencies, less water required compared to water flooding, and low cost compared to the other EOR techniques [Firozjaii Ali Mohsenatabar, Ghassem Zargar, Ezatallah Kazemzadeh, 2018]. Based on these benefits, the present study is focused on polymer flooding. This study is covers the fundamental of polymer flooding and developing of polymer flooding in experimental and numerical simulation cases are discussed.
1.2 PROBLEM STATEMENT
After the conventional water flooding a substantial amount of remaining oil resides in the reservoir due to poor sweep efficiency. Thus it is inevitable to develop new oil production techniques to replace water flooding. Chemical flooding methods such as polymer (such as guar gum) flooding have been shown to be effective in recovering this unswept oil. Polymer flooding is a new technique which is developed out on the basis of alkali flooding, surfactant flooding and polymer flooding [1]. Polymer flooding incorporates the benefits of the above three flooding methods, and oil recovery is enhanced greatly by decreasing interfacial tension, increasing capillary number, enhancing microscopic displacing efficiency, improving mobility ration and increasing macroscopic sweep efficiency.
1.3 AIM AND OBJECTIVES OF THE STUDY
The main aim of this work is to use polymer flooding which is one of enhanced oil recovery (EOR) methods to increase oil production from water flooded fields. The objectives of the study are:
- To carry out a simulation on the use of guar gum in oil recovery.
- To analyze efficiency of polymer flooding for enhanced oil recovery
- To examine the applicability of natural materials for the enhanced oil recovery
1.4 SCOPE OF THE STUDY
There are two types of polymers that can be used in oil recovery. These are synthetic and natural polymers. Synthetic polymers such as hydrolyzed polyacrylamide and natural polymers, such as guar gum. Natural polymer was used because it does not contaminate produced oil. As a result of all adjustments the best possible history match was obtained. The polymer flooding was analyzed and tested on three dimensional, homogenous and flat synthetic model. In the present study an attempt has been made to examine the applicability of natural materials for the enhanced oil recovery.
The petrophysical properties of guar gum polymer obtained from soap nut were measured to find the optimum concentration of polymer and surfactant slugs.
1.5 SIGNIFICANCE OF THE STUDY
In this study it was discovered that polymer flooding used as a mobility control agent provides better volumetric sweep efficiencies in comparison to water flood. Polymer can also be cross-linked to provide an effective water shutoff gels.
1.6 RESEARCH METHODOLOGY
In the course of carrying this study, numerous sources were used which most of them are by visiting libraries, consulting journal and news papers and online research which Google was the major source that was used.
1.7 PROJECT ORGANISATION
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.
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