Investigation of the influences of asphaltene deposition on oilfield development using reservoir simulation

This paper investigates the deposition of asphaltenes in the porous medium of the studied field in Russia and predicts production profiles based on uncertainty evaluation. This problem can be solved by dynamic modeling, during which production profiles are estimated in two scenarios: with and without the activation of the asphaltene option. Calculations are carried out for two development scenarios: field operation under natural depletion and water injection into the aquifer as a reservoir pressure maintenance system. A full-scale compositional reservoir simulation model of the Russian oilfield was created. Within a dynamic simulation, the asphaltene option was activated and the asphaltene behavior in oil and porous medium was tuned according to our own special laboratory experiments. The model was also matched to production historical data, and a pattern model was prepared using the full-scale simulation model. Technological and the asphaltene option parameters were used in sensitivity and an uncertainty evaluation. Furthermore, probable production profiles within a forecast period were estimated. The sensitivity analysis of the pattern model to input parameters of the asphaltene option allowed determining the following heavy-hitters on the objective function: the molar weight of dissolved asphaltenes as a function of pressure, the asphaltene dissociation rate, the asphaltene adsorption coefficient and the critical velocity of oil movement in the reservoir. Under the natural depletion scenario, our simulations show a significant decrease in reservoir pressure and the formation of drawdown cones leading to asphaltene deposition in the bottom-hole area of production wells, decreasing their productivity. Water injection generally allows us to significantly reduce the volume of asphaltene phase transitions and has a positive effect on cumulative oil production. Injecting water into aquifer can keep the formation pressure long above the pressure for asphaltene precipitation, preventing the asphaltene deposition resulted from interaction of oil and water, so this way has higher oil production.

Numerical Simulation of Asphaltene Precipitation and Deposition during Natural Gas and CO_(2) Injection

Asphaltene deposition is a significant problem during gas injection processes,as it can block the porous medium,the wellbore,and the involved facilities,significantly impacting reservoir productivity and ultimate oil recovery.Only a few studies have investigated the numerical modeling of this potential effect in porous media.This study focuses on asphaltene deposition due to natural gas and CO_(2) injection.Predictions of the effect of gas injection on asphaltene deposition behavior have been made using a 3D numerical simulation model.The results indicate that the injection of natural gas exacerbates asphaltene deposition,leading to a significant reduction in permeability near the injection well and throughout the reservoir.This reduction in permeability strongly affects the ability of gas toflow through the reservoir,resulting in an improvement of the displacement front.The displacement effi-ciency of the injection gas process increases by up to 1.40%when gas is injected at 5500 psi,compared to the scenario where the asphaltene model is not considered.CO_(2) injection leads to a miscible process with crude oil,extracting light and intermediate components,which intensifies asphaltene precipitation and increases the viscosity of the remaining crude oil,ultimately reducing the recovery rate.

Lean HC gas injection pilots analysis and IPR back calculation to examine the impact of asphaltene deposition on flow performance

Gas injection is one of the most economical and effective approach to improve oil recovery.However,outcome of such approach is contingent to reservoir heterogeneities impacting gas override and fingering.Furthermore,injected fluid composition and its compatibility with the reservoir fluid potentially impact flow assurance issues such as asphaltene precipitation into the wellbore and surface facilities.The objective of this paper is to examine the lesson learnt from a couple of field scale 5 spot patterned lean hydrocarbon gas injection pilots which were deployed in a heterogeneous carbonate formation of a giant field located offshore Abu Dhabi under secondary and tertiary drive mechanisms.Said pilots provides a valuable insight on production performance,pressure support,gravity override,fluid composition and evidence of asphaltene deposition that resulted in heavy production loss prior to the solvent treatment.This paper presents the overall pilot performance including pattern recovery,fluid front movement,potential role of heterogeneity in gas breakthrough timings and the operational events to witness asphaltene deposition affecting the flow performance.The deposited asphaltene cake thickness was measured mechanically during routine tubing clearance check operation that was helpful in estimating production loss due to altered production tubing flow opening.Also an integrated approach is applied to confirm the AOP laboratory measurements with the actual deposits of asphaltene that were found in to the production tubing.In order to confirm the effect of asphaltene deposition on inflow from near wellbore formation to the wellbore,a straightforward yet innovative nodal analysis approach was applied to study well performance using the calibrated and history matched well model.It was noticed that not only the outflow was altered because of asphaltene deposition into wellbore but also the inflow(productivity index)was seriously impacted potentially due to asphaltene deposition in near wellbore formation.