No abstract

Inadequate wellbore cleaning contributes to several major drilling problems such as; increase in torque and drag that can limit the reach to target, mechanical pipe sticking, difficulties in casing and cementing and logging operations that can increase well cost significantly. Meanwhile, effective removal of drilled cuttings from the wellbore improves penetration rate and drilling efficiency. Herein, water-based mud was formulated with nanosilica to enhance cuttings and solid particles transport from the wellbore to the surface. Four different weight percent concentrations of nanosilica (0.001, 0.003, 0.005 and 0.01 wt.%) at three different flow rates in litres/seconds (0.4, 0.6 and 1.0) and cutting size (small, medium and large) were used to investigate the formulated water-based mud lifting capacity of the drilled cuttings and other solid particles. Thereafter, the hole cleaning efficiency of the water-based mud containing nanosilica was compared to conventional water-based mud. The results show that nanosilica water-based mud influences the cuttings lifting capacity. The addition of the nanosilica concentrations to the water-based mud enhances the viscosity, thereby increasing the muds carrying and circulating capacity. Moreover, nanosilica water-based mud displays mud stability that will stabilize the wellbore and prevent the intrusion of formation fluids into it when compared with the conventinal water-based mud. The effect of cuttings size on the wellbore cleaning is minimal. The large cuttings size shows a lower degree of cuttings transportation compared with the small and medium cutting size. The small cuttings size has higher cuttings recovery to the surface. Finally, though increase in flowrate leads to more cuttings recovery, there is every tendency that much fluid flow rate will cause an increase in frictional pressure losses and equivalent circulating density, high pump pressure requirement and potential hole erosion.

Nigeria is gradually advancing into the secondary stage of oil recovery, necessitating preparation for tertiary oil recovery especially enhanced oil recovery (EOR). Considering the high cost of EOR agents, it is imperative to investigate the performance of available local EOR agents against foreign agents when these agents (such as surfactants and polymers) are used in combination. Oil displacement experiments were thus conducted using foreign and local surfactant-polymer (SP) and alkaline-polymer (AP) agents on Nigerian crude and their results were compared. The experiments entailed using different percentage ratios of surfactants to polymers and alkaline to polymer. Four kinds of Alkaline were also used to displace residual oil from sand to find out what type of alkaline displaces oil better. The displacement efficiencies obtained from experimental results showed that the foreign EOR agents performed better than the local EOR agents. For the SP agents, the foreign SP displaced above 90% of both light and medium crude at about 45/55 percentage and 0/100 percentage respectively. The local SP displaced a maximum of about 35% of the light crude and 75% of medium crude at an SP ratio of about 20/80 for both cases. The use of Alkaline-Polymer results showed that the foreign agents performed better than the local agents. The maximum displacement efficiency of the foreign AP was 78.13% at a ratio of 40/60 while the maximum displacement efficiency of the local AP was 64% at a ratio of 60/40. The displacement of residual oil experiments performed using four kinds of alkaline showed that potassium hydroxide (KOH) enhances recovery better than NaOH, Na2CO3 and Palm bunch ash (a local source of alkaline). It was also observed that oil displacement efficiency increased as pH value of the alkaline increased.

Oil rim reservoirs are often troublesome to produce commercially as a result of the adverse effect of coning and cusping/cresting. In this study, deviated and horizontal wells were employed to determine the optimal well type to be drilled in the "GISO" oil rim reservoir in order to attain optimum oil recovery while reducing uneccessary cost. The GISO oil rim reservoir considered in this study had a thickness of 8ft with grid dimensions of 91×74×20 in the i, j, and k coordinates respectively, and contained a dynamic reservoir oil volume of 9.37MMSTB. Results obtained from simulation revealed that there was not enough oil recovered from the subject oil rim reservoir, owing to the fact that that the reservoir had a very small oil column thickness and this led to the early encroachment of water into the oil column. Three horizontal wells and one deviated well were simulated in the oil rim in order to determine the preferred well type for optimum hydrocarbon recovery for a period of 20 years. The four cases were simulated with a constant production rate of 2000STB/D. Well H1, a horizontal well with lateral length of 272ft recovered 840MSTB, while well H4, a deviated well with a deviated well case with an inclination angle of 84.20° from the GOC and lateral length of 242ft recovered 830MSTB.