Investigating the effect of perforation diameter and carbon dioxide bubble size distribution on heavy oil recovery

Okudolor, AG

Abstract

Global demand for energy is rising steeply because of escalating energy consumption coupled with depleting conventional petroleum reserves. To address this challenge, heavy oil has been considered as a strategic petroleum resource that can be produced intensively to supplement the global supply of conventional hydrocarbons. In recent years, thermal-based techniques, such as cyclic steam stimulation (CSS) and steam assisted gravity drainage (SAGD), have traditionally been used to enhance heavy oil recovery. However, due to shallow pay zones in heavy oil reserves, wellbore heat losses can become excessive, making the process ineffective and uneconomical. For in-situ combustion, high-temperature oxidation reaction model is very challenging to maintain; which inevitably leads to low-temperature oxidation and consequently poor oil recovery. Another method considered for the heavy oil-Enhanced Oil Recovery (EOR) process is chemical flooding. However, the formation of brine with high salinity and divalent ions leads to process inefficiencies.
In this study, experimental techniques have been developed to examine the effect of perforation diameter and CO2 bubble size distribution on the viscosity and recovery of heavy oil during Enhanced Oil Recovery process. To conduct the investigation, an experimental rig was constructed to simulate the flow of CO2 in heavy oil. The oil viscosity, CO2 bubble sizes were measured at different pipe perforation diameters and constant CO2 injection pressure. Also, core flooding experiments were conducted on two reservoir models using a core holder modified to incorporate different perforated seals for the CO2 flooding experiment.
Findings from the first experiment showed a 28% reduction in the dynamic viscosity of the heavy oil when CO2 was injected at a 2.2 bar gauge pressure through a perforation of 0.5 mm in diameter. However, when the seal was replaced with 3 mm centrally perforated seal, the percentage reduction in the dynamic viscosity obtained at 2.2 bar was 5%. In all cases of perforation diameter investigated, the results indicate a direct variation between the perforation diameter and the dynamic viscosity of the heavy oil. In addition, it was observed that the concentration of the CO2 microbubbles in the range of 1-100 µm varied directly with the perforation diameter but inversely with the oil viscosity. In the core flooding experiments, oil recovery improved by 24.5% by changing the perforation diameter to 0.5 from 3.0 mm in the homogeneous model. For the heterogeneous model, the improvement was 16 %. The amount of CO2 utilised in both models also dropped as the perforation diameter was reduced.
An economic analysis of a heavy oil recovery process was conducted using the perforation reduction method typified in this study. The analysis aimed to ascertain the economic viability of the proposed method. Parameters from a heavy oil field were used for the simulation of a model to generate a five-year production data. Two projects were used for the analysis: A and B. Project A represents the heavy oil recovery process without any reduction of the well casing perforation diameter, while project B denotes the recovery process with the reduction of perforation diameter by a factor of six as demonstrated in this study. In both cases, the net present value at a discount rate of 5% and 10% were computed to ascertain their viability. In addition, the payback period for the both viable projects were determined.
Findings from the economic analysis indicated that projects A and B were viable at 5% discount rate with A generating a net present value of 0.1 million US dollars as against B that made 4 million US dollars in five years. At 10% discount rate, only project B was viable, recording a net present value of 3.2 US million dollars. The discounted payback period for project A and B were 2 years, 5 months and 1 year, 2 months respectively. The implication of the different period is that heavy oil production using the reduced perforation diameter (project B) would recover its initial investment in half the time it would take project A.
Finally, the results from both the experimental study and economic analyses show that heavy oil recovery process in sandstone reservoirs can be significantly improved by the application of well completion with smaller perforation diameter.

Citation

Okudolor, A. (in press). Investigating the effect of perforation diameter and carbon dioxide bubble size distribution on heavy oil recovery. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Jun 8, 2018
• Deposit Date: Sep 21, 2018
• Publicly Available Date: Jun 8, 2020
• Additional Information: Funders : Benok Consolidated Limited, Portharcourt Nigeria