Abstract

Some recent research results have shown that especially for long horizontal wells with relatively high rate, when the friction loss plays a significant role, the flow geometry is more appropriate to a hyperbolic rather than an ellipsoid as it is usually accepted in the literature. This flow geometry generates, in the porous media surrounding the horizontal well, a non-symmetrical potential distribution that will affect the fluid displacement along the horizontal section of the well. Thus, the drainage area tends to be greater in the vicinity of the beginning of the horizontal well section and to diminish toward the end of the horizontal section. This will also increase the probability of water and/or gas conning problems in the region of the beginning of the horizontal section. Special attention should be given in this case to the front displacement in a waterflooding process when, do to the potential distribution, the front velocity could be greater at the beginning of the horizontal well section, generating a premature water breakthrough on that direction, the rest the reservoir remaining unflooded. The paper presents a new completion technology that improves the horizontal well performances in the above circumstances. Several numerical results are presented.

Introduction

In the last decade, the interest in horizontal wells increased because these wells offer solutions to the problem of producing oil and gas in reservoirs where conventional technology fails. Some examples are thin reservoirs, reservoirs with gas and/or water coning problems, reservoirs with natural fractures, reservoirs with low permeability and high anisotropy, and reservoirs with poor sweep efficiency. In addition to reducing coning problems, horizontal wells can enhance recovery by larger drainage area.

There are many models to predict the inflow performances of horizontal wells. Part of these models consider cylindrical flow geometry and others consider that the flow geometry is ellipsoidal. Nearly all of them have a common point of view: the flow in reservoir is symmetrical and the flow rate is proportional with the length of the well. There are relatively few technical reports which take into consideration the pressure drop along the horizontal well.

Economics aside, these facts imply that a horizontal well should be as long as possible. However there are some factors which can limit the length of horizontal well. One of them is friction loss in the wellbore. This is the case of long horizontal wells and/or high rates. As a results of the friction losses in the wellbore, the potential distribution in the porous media surrounding the horizontal well is non-uniform. This non-uniform distribution of the potential will generate a non-uniform fluid flux along the wellbore. An unproductive zone can appear in the wellbore as was suggested by Deeken. Also, the conning problem is amplified in such cases.

This paper presents the fundamental aspects for a completion technique to generate a uniform potential distribution around the horizontal section.

To our knowledge this is the first technology which has the objective to minimize the effect of friction losses in the wellbore on the recovery efficiency.

Pressure Drop along the Horizontal Well
Pipe Model

We used the equations presented in Appendix-A to compute the pressure drop along the horizontal section considering a constant rate flowing through a pipe element. The results computed for two pipe diameters of 2 and 3 inches and different oil viscosities are presented in Fig. 1 and respectively Fig. 2.

As one can see, for high and very high flow rates, especially for high viscosity and lower pipe diameters, the pressure losses along the horizontal well can be significant.

P. 619

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