The Effect of Horizontal Well Orientation On Secondary Biopolymer Flooding of Safaniya Crude Oil
Authors: El-Sayed A.H. 
Published: March 2010

Abstract
This paper presents an experimental investigation of the effect of horizontal well orientation on xanthan biopolymer flooding of Safaniya crude oil, in Saudi Arabia, through a horizontal well in laboratory scaled models. Two models were scaled according to two possible horizontal-vertical field arrays to study the effect of horizontal well orientation on oil recovery. A third model was designed for vertical wells only to compare between horizontal and vertical injectors. Different biopolymer concentrations were used to determine the most effective concentration for secondary biopolymer flooding of Safaniya crude oil. Oil recovery and oil cut due to biopolymer injection through a horizontal injector and a vertical injector were undertaken for comparison.
The results showed that displacing Safaniya crude oil with 0.15% biopolymer concentration in the secondary phase yielded the highest oil recovery. A diagonally-oriented horizontal well in the mixed arrays accelerated and increased the oil recovery more than a parallel-oriented horizontal well and a vertical well. A parallel-oriented horizontal well resulted in a larger unswept area which yielded trapped oil in the model and consequently resulted in a lower oil recovery than even a vertical injector.

Introduction
Horizontal-well technology was considered to be the most significant technology in the oil and gas industry of the 1980's(1). Early applications were devoted to exploiting thin reservoirs, reservoirs suffering a high tendency to water cone, and reservoirs of high vertical permeability. Recently, horizontal-well technology was applied in thermal recovery methods, gas injection, waterflooding, chemical flooding, gas storage, and exploiting conventional reservoirs(2–7).
Chemical flooding methods for enhanced oil recovery have a long history, but in the last decade they have received an extraordinary amount of attention from researchers and operators alike. Polymer flooding is one of the methods which has been tested and developed for conventional as well as heavy oil recovery(8–11). Polymer flooding involves the addition of high molecular weight polymers to the injection water to improve the mobility ratio by increasing the viscosity of the water and by reducing the effective permeability of water. This paper addresses the use of biopolymer solutions for the recovery of Safaniya crude oil, which is considered to be heavy crude oil, in the secondary phase of oil recovery through a horizontal well. It also studies the effect of horizontal well orientation on the oil recovery and oil cut.

Literature Review
The application of polymer flooding has been well established, not only in laboratory studies but also in field application, for some time. The history of polymer flooding goes back to the year 1964 when Pye(10) and Sandiford(11) demonstrated that the injection water mobility can be reduced significantly by the addition of a small amount of a water soluble polymer. In 1966, Mungan et al.(12) studied the rheological properties of the flow characteristics of polymer solutions and classified them as pseudoplastic fluids. Later research by Mungan(13) found that the apparent viscosity of partially hydrolyzed polymer solutions was affected by temperature; thermal degradation occurred between 135 °C and 300 °C.