An Experimental Approach of Influences of Perforated Length and Fractures on Horizontal Well Productivity
Authors: Shedid S.A. , Zekri A.Y. 
Published: March 2010

Many simulation studies have been conducted regarding the importance of perforated well length on horizontal well performance. All of these studies suffered from their dependence upon theoretical models, which lack plausibility due to the lack of accurate experimental and/or field data. Therefore, there is a real need for experimental data to be used for tuning the single well simulation models before applying a full field simulation of oil reservoirs with horizontal wells.

This experimental study was designed to investigate the influences of fractions of perforated length, total length, and fractures, which do not intersect with a well axis, on the productivity of horizontal wells. An experimental model (60 cm x?40 cm × 20 cm) was designed and used to achieve the study objectives. Carefully sized sandpacks were used to represent the homogeneous unconsolidated porous media while a perforated aluminum sheet was used as a horizontal fracture parallel (horizontal fracture) and perpendicular but not intersecting (vertical fracture) the horizontal well axis in the sandpack. Several runs were carried out using horizontal wells with different lengths and different perforation fractions of total length utilizing homogenous porous media with and without fracture systems.

The results indicated that an increase of perforated well length increases flow rate of the horizontal well for both homogeneous and fractured formations that do not intersect with the well axis. Furthermore, horizontally-fractured formations parallel to and vertically-fractured formations vertical to the well axis improve the productivity of horizontal wells for different perforation ratios. A single vertically-fractured porous medium provides a higher productivity ratio than a horizontally-fractured one for the same perforation length and intensity, when both fracture systems do not intersect with the well axis. Several empirical equations were developed to correlate the horizontal well productivity with perforated length for homogenous and fractured porous media.

Ignoring of the effect of pressure drop along horizontal well may have serious implications on perforated well length since proportionality of the productivity index to the well length is no longer valid.

Introduction and Literature Review

Recently, the economic feasibility of drilling a horizontal well improved drastically due to advances in drilling technology. Advantages of horizontal wells over vertical well applications have been confirmed by many scientists(1–4) and operators(5–7). Horizontal wells showed many distinct advantages over vertical ones such as improvement of well productivity, attenuation of sand production, and significant reduction of gas and/or water coning problems.

From reservoir and production engineering standpoints, the sole difference between vertical and horizontal wells was identified to be the contact area. For a partially penetrating vertical well, the reservoir disturbance due to a vertical well was limited to the close vicinity of the wellbore hole(8). Then, the choke diameter became the main parameter affecting the flow rate. For a horizontal well, the disturbance created by the well not only affected the vicinity of the wellbore, but also influences the whole reservoir due to the greater contact area of the pay zone penetrated by the well.