Effect of Horizontal-vertical Well Configuration On Oil Recovery By Alkaline Flooding
Authors: El-Sayed A.A.H. , Almalik M.S. 
Published: March 2010

Abstract
This paper presents- an experimental investigation of the! effect of horizontal-vertical well configuration on oil recovery of Safanyia crude by alkaline flooding. Emphasis was focussed on the effect of horizontal well pattern on oil recovery. Also, the effects of three types of alkali solutions; sodium- carbonate; (Na2CO3) sodium ortha-silicate (Na4SiO4). and sodium hydroxide (NaOH) on cumulative oil recovery, in both secondary and tertiary processes using linear model, vertical- vertical two dimensional model, and horizontal-vertical schemes, were investigated.
It was found that displacing Safanyia crude oil by NaOH solution having 1% concentration results in higher oil recovery in both linear and horizontal-vertical schemes. The highest oil recovery through horizontal-vertical schemes was obtained by, placing the horizontal well perpendicular to the line connecting the two vertical wells with a length that does not reach the boundary of the reservoir- Also, it was found that oil displacement efficiency in the tertiary process is higher than in the secondary process.

Introduction
The use of horizontal wells has been increasing very rapidly throughout the oil industry as advances in drilling techniques continue. In many reservoirs, horizontal wells can solve a number of oil production problems. However, in spite of a tremendous increase in literature references, little information is available on horizontal well applications in enhanced oil recovery (EOR) methods(1). Many published articles show that horizontal wells are still used primarily to solve specific production problems, These include low permeability formations especially fractured formations low permeability gas reservoirs, unusual gas sources, gas or water coning, thin formations, and viscous oil(2,3).
Most horizontal well applications of EOR activities have been in the area of thermal recovery, primarily for steam stimulation and steam drive(4,5). Although there is relatively little published information on the use of horizontal injection wells, other than thermal recovery the for patterns of both horizontal injection and vertical production well, to increase the rate of flooding in EOR has been mentioned(6,9). Early laboratory work oncaustic flooding through horizontal wells (10) showed that the use of a horizontal wellas an injector in alkaline flooding increased oil recovery by a minimum of 8% o initial oil-in-place (IOIP) compared to vertical wells.
This paper studies the effect of horizontal 0vertical well configurations in one uater of a five-spot pattern model on oil recovery by alkaline flooding. It also discusses the effect of alkaline type and concentration on oil recovery in secondary and tertiary processes. The study was not made ina scaled model. Instead, Safanyia crude oil from Saudi Aramco has been used to investigate qualitatively the effect of horizontal-vertical well configuration in one quarter a five-spot model.

Experimental Work

Fluid Properties
The physical properties of the fluids used in this study are shown in Table 1. The crude oil is Safanyia crude received from Saudi Aramco. The oil has an acid number of 1.5 mg KOH/g crude oil. The oil acidity was measured according to IP 1/74 test analysis which is equivalent to ASTM D974 test (11).