Water/oil cresting in horizontal wells : a sensitivity study

This work presents a rigorous sensitivity analysis on cresting using a physical model, to investigate the effects of varying inclined section of horizontal well, lateral length in reservoir and oil viscosity on oil recovered, cumulative of water produced and Water Cut in thick- and thin-oil rim homogeneous reservoirs faced with strong bottom aquifer and considerable gas cap. From the results, it was observed that the geometry of the horizontal well and location of the bottom water injection points significantly influence the cumulative liquid produced, particularly in thin-oil rim reservoirs. The cumulative water produced and cumulative Water Cut were found to increase with increase in oil viscosity. The oil recovered from the thin-oil rim reservoir, were as high as 17.84% and 24.92% for oil viscosity of 50 cP and 100 cP respectively whereas 19.15% and 13.93% were observed for cumulative water produced from the thick-oil rim reservoir at 50 cP and 100 cP respectively

Effectively optimizing production of horizontal wells in homogeneous oil reservoirs

Horizontal well applications have been predominant since their conception, for reasons such as effective depletion of oil reservoirs and especially in water cresting, gas cresting or water and gas cresting applications due to the casings enhanced exposure to the reservoir. Cresting is hugely dependent on oil production rate, pressure drawdown and can negatively influence the degree of depletion as well as the overall recovery efficiency of oil reservoirs. This paper presents a novel procedure of mimicking horizontal wells aimed at investigating experimentally the effect of varying inclined sections (having different vertical and horizontal displacements) of horizontal wells at low angles of inclination (15o-30o) in a homogeneous reservoir underlain by a strong bottom aquifer and overlain by a considerable gas cap drive occurring simultaneously. The results for the performance of the different horizontal well geometries in terms of cumulative oil recovery and Water-Oil-Ratio; over a fixed liquid production time were compared. From the results obtained, it was observed that the short radius well with 30o angle of inclination and ratio of vertical displacement of the inclined section to reservoir height of 0.07 resulted in the highest oil recovery of 38.73%. Using the presented procedure, 5.60% increment in oil was recovered with 11.40% reduction in cumulative produced water were observed between the best and worst cases from the same reservoir. At higher withdrawal rates and pressure drop, long radii wells are recommended due to cresting delay ability while improving oil recovery

Effect of impermeable barrier orientation on bottom water cresting

The use of either a permeable or semi-permeable barriers has been proven to be effective in minimizing cresting effects in oil reservoirs characterized by strong bottom aquifer, with the latter known to be more effective. Most research has been focused on coning control in vertical wells with little research existing for cresting control in horizontal wells, especially in use of barriers. Therefore, this paper sets out to numerically investigate the effect of an impermeable barrier orientation in an oil reservoir characterized by a strong bottom aquifer. The orientations considered in this study were horizontal and inclined (step-like) in terms of placement in the oil reservoir, modeled with similar thickness and width. From the results, it was observed that a horizontally-placed impermeable barrier is more effective than inclined impermeable barriers in bottom water cresting scenarios. A horizontal impermeable barrier closer to the perforation of the horizontal well, 0.08x in thickness to the reservoir height and 0.45x to reservoir width was the most effective, although the effect of impermeable barrier width was found to be inconsistent with the performance of impermeable barriers. The study shows that the closer the entire top surface of the inclined impermeable barrier, the more effective the inclined impermeable barrier in minimizing bottom water cresting effect. The value of Reynolds number was found to be dependent on the orientation, thickness, position, and width of an impermeable barrier

Economic evaluation of environmentally friendly vegetable oil-based invert emulsion

Stringent environmental regulations and technical requirements of difficult formations such as shale demand the use of functional mud system to complete a well safely and economically. The economic viability of 50/50 oil-water ratio invert emulsion which uses vegetable oil and egg yolk as a non-toxic emulsifier was evaluated. The evaluation showed less cost of mud formulation by 67% and disposal by 47.5%. This equate to saving of $55.82 per barrel of invert emulsion formulated and$28.50 per barrel disposed. The low oil-water ratio mud is viable for low fluid loss for enhanced wellbore stability and less oil retained on drilled cutting

50/50 oil-water ratio invert emulsion drilling mud using vegetable oil as continuous phase

Formulation of a low oil-water ratio drilling mud with vegetable oil continuous phase without adversely affecting the mud rheology and stability has been a major challenge. A low oil-water ratio is beneficial in producing low fluid loss which is essential for wellbore stability. This study examined the possibility of 50/50 oilwater ratio invert emulsion drilling mud using a vegetable oil continuous phase. Jatropha oil was used as continuous phase. 12 ml of egg yolk which was separated from the albumen was added as the primary emulsifier additive. The rheological, stability and filtration properties were examined. The plastic viscosity and yield point were found to be 36cp and 17 Ib/100 ft2 respectively. The electrical stability at 48.9ºC was 353v and the 30 minutes fluid loss was 6ml. The results compared favourably with a similar formulation using 70/30 oil - water ratio giving plastic viscosity of 31cp, yield point of 17 Ib/100 ft2, electrical stability value of 480v and 12ml for the 30 minutes fluid loss.This study indicates that with a good mud composition using guided empiricism, 50/50 oil-water ratio invert emulsion drilling mud is feasible with a vegetable oil continuous phase. The choice of egg yolk as emulsifier additive is for compatibility with the vegetable oil and environmental concern. The high water content with no fluid loss additive will also minimise the cost of mud formulation

An investigation into the volumetric flow rate requirement of hydrogen transportation in existing natural gas pipelines and its safety implications

As an alternative to the construction of new infrastructure, repurposing existing natural gas pipelines for hydrogen transportation has been identified as a low-cost strategy for substituting natural gas with hydrogen in the wake of the energy transition. In line with that, a 342 km, 36″ natural gas pipeline was used in this study to simulate some technical implications of delivering the same amount of energy with different blends of natural gas and hydrogen, and with 100% hydrogen. Preliminary findings from the study confirmed that a three-fold increase in volumetric flow rate would be required of hydrogen to deliver an equivalent amount of energy as natural gas. The effects of flowing hydrogen at this rate in an existing natural gas pipeline on two flow parameters (the compressibility factor and the velocity gradient) which are crucial to the safety of the pipeline were investigated. The compressibility factor behaviour revealed the presence of a wide range of values as the proportions of hydrogen and natural gas in the blends changed, signifying disparate flow behaviours and consequent varying flow challenges. The velocity profiles showed that hydrogen can be transported in natural gas pipelines via blending with natural gas by up to 40% of hydrogen in the blend without exceeding the erosional velocity limits of the pipeline. However, when the proportion of hydrogen reached 60%, the erosional velocity limit was reached at 290 km, so that beyond this distance, the pipeline would be subject to internal erosion. The use of compressor stations was shown to be effective in remedying this challenge. This study provides more insights into the volumetric and safety considerations of adopting existing natural gas pipelines for the transportation of hydrogen and blends of hydrogen and natural ga