Abstract

Although application of horizontal well technology is categorized as a relatively new and expensive but it has been proven more effective and efficient in producing oil. However, the production rate strategy to obtain optimal result has not been well developed due to the difficulties to identify the influence and interaction of forces related to fluid flow mechanisms in reservoir. Particularly for oil reservoir with bottom water drive, the movement of water-oil contact/interface in a reservoir is strongly affected by interaction of the acting forces, such as: viscous force, gravity force and capillary force.

The main objective of this research is to study and investigate the influence of the forces interaction on production performance of the horizontal well producing oil from bottom water drive reservoir. For this purpose, a physical scaled model has been successfully constructed to simulate the production performance. Scaling down and construction of the model are performed by using dimensional analysis.

Results show that the interaction of the forces in the reservoir strongly affects the well production, in which the production performance increases as the ratio of gravity to viscous forces increases for all cases examined. Meanwhile, the changing of capillary force, which was believed by several researchers that it has no pronounced effect to the fluid flow mechanism in the reservoir, shows significant effect to the production performance of the well. The influence of reduced capillary forces in reservoir will enhance the well production performance. Consequently, in term of the ratio of gravity to capillary force, an increase in the ratio tends to improve the oil recovery.

Introduction

A well producing from bottom water drive reservoir, the oil production usually followed by water production. This situation occurs when bottom water has broken through the wellbore. In most cases, the use of conventional vertical well to produce oil from such reservoir always faces severe water coning condition. This is because the actual production rate highly exceeds the critical rate, defined as a rate above which the flat surface of oil-water interface starts to deform. Water coning itself is a phenomenon of bottom water intruding the oil zone such that the invaded oil zone resembles a cone. This is usually termed water cresting for horizontal well.

The application of horizontal well technology has been widely used in many countries to improve oil recovery from bottom water drive reservoirs1–5. It can be achieved since at low drawdown horizontal well can deliver a larger capacity to produce oil compared to conventional vertical well. Thus, the critical rate in a horizontal well can be higher than that in vertical well. But in practice, production rate is usually higher than the critical rate, even in horizontal well, due to economic considerations. When this takes place, high mobility bottom water will invade crestingly into the overlying oil zone and move toward to the wellbore resulting in lower displacement efficiency or oil recovery. The problem is then how to do the production strategy so that not only producing the well at considerably higher rate but also the high oil recovery can be achieved. This can be done if the fluid flow mechanism as the results of interaction of forces in the reservoir is fully understood. During well production, three different forces work in the reservoir; they are viscous force, gravity force and capillary force.

Complex mechanism of fluids flow in a reservoir system containing a horizontal well and in the wellbore itself are not well understood yet. Tackling such problem, several researchers therefore simulated into the physical model6–10. Most of the researchers used the well-known Hele-Shaw model similar to the one employed by Meyer and Searcy11 studying water coning behavior for vertical well. Consequently of using this model is that the role of capillary pressure in the system cannot be studied since the gap between the plates so wide that the capillary force is negligible.

The objective of this research is therefore to study and investigate the influence of the forces interaction on production performance of the horizontal well. To meet this objective, the physical model using consolidated sandpack was developed.

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