TY - THES

T1 - Polymer Flooding Optimization in a Romanian Field

AU - Sugar, Antonia-Bogdana

N1 - no embargo

PY - 2018

Y1 - 2018

N2 - As previous attempts of water injection in the Romanian field, Vata, showed poor results mainly due to an unfavourable mobility ratio, the attention was shifted on finding different alternatives to increase incremental oil production. An EOR screening process, using both conventional and advanced methods, was performed and polymer flooding resulted to be one of the proposed options. On these grounds, an estimation of polymer flood efficiency for this field represents the scope of this study. The availability of an already existing reservoir model for the region investigated, including the history match of observed data and prediction cases for water injection, made possible the polymer flooding evaluation on a simulation basis. This paper presents the first simulation results of polymer flood in this reservoir; therefore the polymer-rock interaction parameters used as input were taken from an analogous field, where polymer core flood experiments were available. The operating parameters used for the simulated cases, namely injection flow rate, polymer concentration and slug size, were chosen mainly based on technical reasons still, in the decision making process, the economic viability of the polymer project was taken into account by dint of utility factor. A sensitivity analysis on polymer adsorption, permeability reduction and inaccessible pore volume influence on recovery factor was first performed, in order to assess simulation results’ degree of uncertainty and the interval limits of production characteristics. Recovery factor showed to be almost insensitive to inaccessible pore volume; on the other hand permeability reduction was found to have the highest influence inducing up to 20% variation in RF. One focus of the study was represented by comingle polymer injection viability evaluation as the field consists of 5 different layers. The analysis was performed on a layer region basis, including also the Non-Newtonian behaviour of polymers for increased accuracy. The observation that the deepest region, A Sand 2, and a big part of region A Sand 1, were almost untouched by polymer solution as result of poor rock quality, suggests that comingle injection should not be considered without further investigation. A closer look to polymer behaviour showed that considering Non-Newtonian rheology, the field recovery factor for the 1500ppm polymer concentration case was equal to 1000ppm concentration and Newtonian behaviour scenario. This remark involves a downturn of expected flood effectiveness. Polymers are known to be sensitive to harsh environments and the investigated field falls into the category of high saline reservoirs. Total dissolved solids of up to 90 000ppm had been reported throughout the years and due to lack of accurate measurements a specific narrower salinity range cannot be defined. On this basis, salinity effects, from 50000 ppm up to 90000ppm, on recovery factor were investigated and meaningful variation was determined by using different viscosity yield curves. Taking into account the impact on economics, a higher concentration of conventional or TDS tolerant polymers should be considered. The results concluded that polymer flooding could indeed represent a viable option to increase production in Vata field. For future evaluations it is recommended that in addition to heterogeneity capturing via multiple realization modelling, also SCAL and polymer core flood experiments as well as water salinity measurements should be conducted.

AB - As previous attempts of water injection in the Romanian field, Vata, showed poor results mainly due to an unfavourable mobility ratio, the attention was shifted on finding different alternatives to increase incremental oil production. An EOR screening process, using both conventional and advanced methods, was performed and polymer flooding resulted to be one of the proposed options. On these grounds, an estimation of polymer flood efficiency for this field represents the scope of this study. The availability of an already existing reservoir model for the region investigated, including the history match of observed data and prediction cases for water injection, made possible the polymer flooding evaluation on a simulation basis. This paper presents the first simulation results of polymer flood in this reservoir; therefore the polymer-rock interaction parameters used as input were taken from an analogous field, where polymer core flood experiments were available. The operating parameters used for the simulated cases, namely injection flow rate, polymer concentration and slug size, were chosen mainly based on technical reasons still, in the decision making process, the economic viability of the polymer project was taken into account by dint of utility factor. A sensitivity analysis on polymer adsorption, permeability reduction and inaccessible pore volume influence on recovery factor was first performed, in order to assess simulation results’ degree of uncertainty and the interval limits of production characteristics. Recovery factor showed to be almost insensitive to inaccessible pore volume; on the other hand permeability reduction was found to have the highest influence inducing up to 20% variation in RF. One focus of the study was represented by comingle polymer injection viability evaluation as the field consists of 5 different layers. The analysis was performed on a layer region basis, including also the Non-Newtonian behaviour of polymers for increased accuracy. The observation that the deepest region, A Sand 2, and a big part of region A Sand 1, were almost untouched by polymer solution as result of poor rock quality, suggests that comingle injection should not be considered without further investigation. A closer look to polymer behaviour showed that considering Non-Newtonian rheology, the field recovery factor for the 1500ppm polymer concentration case was equal to 1000ppm concentration and Newtonian behaviour scenario. This remark involves a downturn of expected flood effectiveness. Polymers are known to be sensitive to harsh environments and the investigated field falls into the category of high saline reservoirs. Total dissolved solids of up to 90 000ppm had been reported throughout the years and due to lack of accurate measurements a specific narrower salinity range cannot be defined. On this basis, salinity effects, from 50000 ppm up to 90000ppm, on recovery factor were investigated and meaningful variation was determined by using different viscosity yield curves. Taking into account the impact on economics, a higher concentration of conventional or TDS tolerant polymers should be considered. The results concluded that polymer flooding could indeed represent a viable option to increase production in Vata field. For future evaluations it is recommended that in addition to heterogeneity capturing via multiple realization modelling, also SCAL and polymer core flood experiments as well as water salinity measurements should be conducted.

KW - polymer flooding

KW - sensitivity analysis

KW - Newtonian and non-Newtonian

KW - commingle injection

KW - water salinity

KW - Polymerinjektion

KW - Sensitivitätsanalyse

KW - newtonsch und nicht- newtonsch

KW - Salinität

M3 - Master's Thesis

ER -