Abstract

The world still contains tremendous heavy oil resources. Ever-increasing energy demand requires more attention to be paid to harvesting all hydrocarbon resources, including heavy oil. The use of thermal processes has proven by far the most effective approach in producing heavy oil.

This paper proposes a practical steam stimulation strategy for heavy oil development using horizontal wells. In the proposed process, steam is cyclically injected through a horizontal well pattern to heat near wellbore reservoirs, and after a period of cyclic steam stimulation, one of the pattern wells is converted to a steamflooding well and the other pattern well is converted to a production well.

Through 3D reservoir simulation, this paper compares production performance of the proposed strategy with conventional cyclic steam stimulation (CSS), steamflooding (SF), and steam-assisted gravity drainage (SAGD).

A sensitivity analysis is also conducted to study the effect of oil viscosity and reservoir permeability on horizontal well production performance under different production strategies.

Introduction

Resources of heavy oil and natural bitumen (in oil sand reservoirs) far exceed the existing light oil reserves. North America has 35 billion barrels of original heavy oil reserves and about 1.7 trillion barrels of demonstrated resources of natural bitumen in oil sand reservoirs[1] . Thermal recovery techniques are by far the most extensively adopted enhanced oil recovery (EOR) process in heavy oil development.

Horizontal well technology has created new opportunities in the implementation of conventional thermal recovery processes. How to efficiently use horizontal well technology in developing heavy oil resources? Pilot test can help answer the question, but such tests are often very expensive. As an efficient way, reservoir simulation plays a very important role in optimizing horizontal well steam stimulation design before a pilot test or full-field development.

CSS and SF have been widely used and are pretty mature techniques. SAGD is gaining more and more attention. There are lots of studies about CSS, SF, and SAGD applications with horizontal wells. This paper proposes a process, horizontal well CSS followed by SF. Through three-dimensional reservoir simulation, this paper compares horizontal well production performance in thermal processes of CSS, SF, SAGD, and CSS followed by SF. The effect of oil viscosity and reservoir permeability on production performance is also studied.

The observations and results from this study will provide important guide to field application of horizontal well steam stimulation in developing heavy oil reservoirs.

Simulation Model and Parameters

The simulation model and parameters are described below. Some parameters are taken from the well-known Fourth SPE Comparative Solution Project[2].

Reservoir Model

The reservoir of interest has a depth of 1500 ft, length of 1050 ft, and width of 420 ft, for this simulation purpose. Vertically, the reservoir has 11 layers with 3 ft for each layer. The initial reservoir pressure and temperature are 75 psia and 125 oF respectively. The initial oil saturation is 55% and the initial water saturation is 45%. The reservoir model data are summarized in Table 1.

Fluid Properties

Regarding water properties, we assume pure water and use standard properties. The oil is a 14 oAPI heavy oil with density 60.68 lbm/ft3 at standard condition. Compressibility is 5x10-6 psi-1 . The coefficient of thermal expansion is 3.8x10-4 oR-1 . The specific heat is 0.5 Btu/lbm-oR. Molecular weight is 600. Temperature and viscosity data are shown in Table 2(a).

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