Abstract

Horizontal drilling has revolutionized the petroleum industry's exploitation of low productivity reservoirs such as heavy oil, tight and naturally fractured reservoirs, reservoirs with gas and/or water coning problems, as well as EOR applications. This paper studied only applications of horizontal wells in low productivity conventional heavy oil reservoirs under primary production. Currently, there are many field applications of horizontal well technology in Saskatchewan heavy oil reservoirs. The performance from horizontal wells drilled in heavy oil reservoirs to date is generally very encouraging. Although horizontal drilling technology is generally understood. there are still some key questions concerning the effective application of horizontal wells in heavy oil reservoirs.

The objective of this paper is to study the impact of key parameters of the horizontal well design using a complete reservoir model which incorporates pressure drop in the horizontal wellbore. Several practical cases were studied for heavy oil reservoirs with viscosity ranging from 100 to 10000 cP. The key parameters evaluated included wellbore length and diameter. The results will be described in terms of oil production, costs and economic profitability.

Results indicated that longer horizontal wells were more desirable than shorter wells due to larger drainage areas translating to higher reserves productivity. Wellbore diameter has a more significant impact on reservoirs with heavier crude oil. The pressure drop in horizontal wells had no significant impact all productivity in heavy oil reservoirs. Therefore, it is more likely that ill the future, we will see longer length and smaller diameter horizontal well applications in heavy oil reservoirs.

Introduction

There are more than a thousand horizontal wells world-wide, and more than 150 horizontal wells are producing in Canada (1). Their popularity continues to grow. Applications of horizontal well technology in low productivity reservoirs, such as heavy oil pools have not only shown higher production rates compared to vertical wells (2), they also have tended to reduce sanding due to larger contact area with the formation causing a lower fluid velocity near the wellbore (2 and 3). In heavy oil reservoirs with water coning problems, horizontal wells have shown higher recovery than vertical wells (4). Although the success of the horizontal well technology in the heavy oil pool development has been very encouraging, there is still much discussion on how to design horizontal wells effectively for heavy oil applications.

There are still some questions regarding the key parameters in horizontal well design. They are the following:

  1. Does the length or the diameter of the wellbore cause a significant pressure drop due to friction loss along the wellbore (impacting the well productivity)?

  2. What is the optimum wellbore diameter for a desired production rate?

  3. What is the role of viscosity undetermining optimal well length or diameter?

To be able to answer the above questions, this study was divided into two parts. The first part evaluated, the flow mechanics and recovery processes of several heavy oil projects using horizontal well technology. The second part is an economic analysis which uses cashflow model to find the optimum profitability for a given project. Conclusions were then derived. using a combination of technical and economic analysis.

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