Conclusion

In this thesis, a novel experimental procedure was presented for investigating the performance of horizontal wells with varying horizontal and vertical displacements of the inclined section. A novel procedure for cresting control in homogeneous oil reservoirs involving the use of electromagnetically operated valve and effluents breakthrough time was also presented. A rigorous sensitivity analysis was performed involving parameter such as varying lengths of inclined sections, lateral lengths in reservoir and oil viscosity. Numerical models were also considered for cresting investigation and validation using CFD and DynamicStudio softwares. From the results presented it can be concluded that:

 The steepness of the inclined section is important in optimizing the productivity of horizontal wells in oil reservoirs affected by severe water cresting, irrespective of the lateral length in the reservoir.

 The higher the pressure drop, the higher the cumulative water cut due to a higher mass withdrawal rate at any given point in time because the mobility of fluid depends on the pressure drop (Section 4.2.2).

 Increased oil recovery efficiency and least water production rate can be achieved using the procedure for varying the inclined section. The performance at the inclined section of a horizontal well depends on the angle of inclination and its vertical displacements. For a given geometry, the higher the angle of inclination, the lower the vertical displacement of the build section due to increasing angles towards the horizontal plane (Section 3.2.1, Table 3-1).

 Using the procedures outlined in this study (Section 4.2 and 4.3), reservoir Engineers can have better understanding as to how production can be effectively optimized in oil reservoirs that are affected by cresting problems. An increment of 6.53% (177.75 cm3_{) in oil recovery (Section 4.2.3) and 11.40% (258 cm}3_{) reduction in cumulative}

water produced (Section 4.2.1, Table 4-1) was achieved at a short simulation time while a 20.14% (356 cm3) reduction in cumulative water produced (Section 4.2.5)

and 8.48% (250 cm3) increase in oil recovery (Section 4.2.4) was realized at longer production time for thick-oil rim reservoirs and longer lateral length. Further increases in oil recovery of 3.56% (108.91 cm3) (Section 4.2.9.1) and a reduction in cumulative water produced of 9.9% (183.99 cm3) (Section 4.2.9.2) were observed for thick-oil rim reservoirs using the cresting control procedure, as discussed in this research work. Increment in oil produced of 163 cm3(Section 4.3.1, Table 4-14) and 134 cm3 cumulative reduction in produced water (Section 4.3.2, Table 4-15) were observed from varying the inclined section of the horizontal well at Vd/Hr equals

0.079 in thin-oil rim reservoirs, at a simulation time of 210 s while a lower oil increment of 6.84 cm3 (Section 4.3.5.1) and cumulative water reduction of 10.98 cm3 (Section 4.3.5.2) were observed when controlled proactively in thin-oil rim reservoirs.

 In general, the shorter the measured depth of horizontal wells, the higher the cumulative water produced, irrespective of oil viscosity. At post breakthrough, the cumulative water produced depends on the measured depth of the horizontal well (Sections 4.2.5 and 4.3.2).

 Experimentally, the cumulative water produced and oil recovered for horizontal wells depend on the location of the bottom water injection points (Sections 4.2.4 to 4.2.6 and 4.3.1 to 4.3.2). The further the horizontal displacement from the farthest injection point, the lower the cumulative water produced at the same operating pressure and liquid production time.

 The shape of the water and gas crest depends on the location of the horizontal well perforations and distance of the lateral well length in the reservoir (Sections 4.2.4 to 4.2.6 and 4.3.1 to 4.3.2).

 Short radii wells are recommended for applications in reservoirs with cresting problems (Sections 4.2 and 4.3). Shorter radii wells are characterized by higher liquid withdrawal rate; higher volumes of water produced but lower average cumulative water cut.

 Thin-oil rim reservoirs reach incredibly high cumulative water cut values in shorter production time unlike thick column reservoirs at the same operating condition

(Section 4.3.3). At the same operating condition, reservoir condition and production time, the closer the WOC is to the GOC the higher the cumulative water produced and cumulative water cut.

 The feasibility of the cresting control procedure is believed to depend on reservoir thickness of the oil column, breakthrough time. The longer the shut-in periods the higher the oil recovery and the lower the cumulative water produced due to the longer time required for the pressure drop to supersede the hydrostatic pressure at the WOC. The wider the reservoir sizes the longer the time required for water and gas to recede after shut-in. The GOC level receded almost immediately when compared with WOC due to its relatively low density and viscosity compared to that of water. The thicker the oil column height the more the oil recovered and less the cumulative water produced. The longer the shut-in duration the higher the oil recovered, the lower the cumulative water produced and the lower the cumulative produced liquid (Sections 4.2.9.1 to 4.2.9.3 and 4.3.4.1 to 4.3.4.3).

 The CFD analysis demonstrated that the cresting effect depends on oil production rate and effective porosity. The lower the viscous resistance and the higher the oil production rate. The WOC and GOC apices increased with increase in simulation time towards the perforation of the well (Sections 5.5.1.2 to 5.5.1.3).

 CFD is a useful simulation tool for cresting prediction and validation of a physical model. However, the over predicted results obtained in terms of validation with the experimental model are due to the isotropic nature of CFD models in terms of flow through porous media (Section 5.5.3).