Minimizing formation damage for preformed particle gels treatment in mature reservoirs

This research studied the effect of preformed particle gels (PPGs) on unswept, low-permeable zones/areas. The objective was to find methods that minimized the damage caused by PPGs on unswept, low-permeable zones/areas, thus improving PPG treatment efficiency. These results can help to identify of the best PPG types, particle sizes, and brine concentrations for specific reservoirs and treatments. This study used sandstone core samples with various degrees of permeability. Two types of particle gels, a strong Daqing gel (DQ) and a weak Liquiblock™ 40k gel (40K), were used, each with a different strength. This research included two stages. Firstly, both a static filtration test model and load pressure model were used to evaluate the damage caused by various PPGs on low-permeability sandstone cores. These results were analyzed using quantitative analytical model. This approach identified the type of PPG that can neither penetrate into conventional solid rocks nor form cakes on the rocks\u27 surface. Secondly, the permeabilities of various packed PPGs with different particle sizes and brine concentrations were measured during the second stage of the research. Static filtration models with both various load pressures and various back pressures were used to measure the permeability of a gel pack. Weak PPGs with smaller particles were proved less permeable than strong PPGs with larger particles. The permeability of the gel pack decreased when both the load pressures and the back pressure increased. In addition the both gel compressibility and water loss was measured. Gel strength was measured before and after compression --Abstract, page iii

Literature Review of Water Alternation Gas Injection

The Water Alternating Gas (WAG) process is a cyclic method of injecting alternating cycles of gas followed by water and repeating this process over a number of cycles. WAG injection is to improve oil recovery, by both increasing the macroscopic and microscopic sweep efficiency and to help maintain the reservoir pressure. Also, WAG injection is to postpone the gas breakthrough. The WAG process provides mobility control in fast zones which extends gas project life and oil recovery. This paper provided a comprehensive literature study about  WAG injection. This  paper has collected most of the requirements of the petroleum engineers that has to know about the WAG injection started from basic concepts until the design parameter for WAG injection

Comparison of Different Gases Injection Techniques for Better Oil Productivity

There are many known enhanced oil recovery (EOR) methods and every method has its criteria to use it. Some of those methods are gas injection such as CO2 injection, N2 and hydrocarbon gas injection. Where the CO2 has been the largest contributor to global EOR. Gas injection can be classified into two main types; continues gas injection (CGI) and water alternating gas injection (WAG). The objective of this research is to propose initial gases injection plan of the X field to maximize the total oil recovery. The feasibility study of different gases to maintain pressure and optimize oil recovery have been examined on a simple mechanistic reservoir model of considerably depleted saturated oil reservoir. In order to maximize the total oil recovery, the simulation study was conducted on 3-phase compositional simulation model. For more optimization, a sensitivity study was conducted on the injection cycling and component ratios. A sensitivity study was also conducted on the following parameters to study their effects on the overall field’s recovery such as flow rate and bottom-hole pressure. Results obtained in this paper shows that, the WAG CO2 injection was found to be significantly more efficient than different gas injection and continues gas injection. The oil recovery depends not only on the fluid-to-fluid displacement but also on the compositional phase behavior.

Effect of Back Pressure on the Gel Pack Permeability in Mature Reservoir

Excess water production has become a significant problem for oil field operations as reservoirs mature. In mature oilfields, gel treatments are using preformed particle gels (PPGs) to reduce fluid channels through super-high permeable formations. As a result, water production decline and sweep efficiency improve. The achievement of the best PPGs treatment mainly depends on whether or not PPGs can successfully reduce the permeability of the channels to the level that we expect. The objectives of this work are to determine what factors influence the blocking efficiency of PPG on fluid channels. It will determine what factors effecting on PPGs pack permeability. A transparent model was designed to observe the compression of gel particles in fluid channels at different back pressures, and thus to study the effect of different parameters on PPG blocking efficiency. PPG pack in the fluid channels affected by the back pressure. It was determined that the increase of the back pressure decreased the PPG pack permeability. Gel pack is compressed and its permeability is reduced as back pressure increases. A permeable gel pack was formed in fluid channels by gel particles. The permeability of the gel pack depended on particle strength, particle size, and back pressure. The results can be used to optimize a PPG design

Experimental Work to Determine the Effect of Load Pressure on the Gel Pack Permeability of Strong and Weak Preformed Particle Gels

Preformed particle gels (PPGs) have been widely applied to reduce the permeability of super-high permeability streaks/fractures. PPGs have an ability to decrease water production and increase sweep efficiency in mature oilfields. Either the success or failure of a PPG treatment depends largely on whether or not PPGs can effectively reduce the permeability of the fluid channels to an anticipated level. This work sought to investigate the influence of several factors on PPG blocking efficiency. A filtration model was designed to determine the permeability of PPGs packed in channels/fractures. Two types of PPGs were used for these filtration experiments: Daqing (DQ) and LiquiBlock™ 40 K. Particle sizes fell between 30 and 120 meshes. Results indicate PPG permeability decreased as load pressure increased. Additionally, PPGs with a larger particle size exhibited higher PPG pack permeability than PPGs with a smaller particle size. The PPG permeability with a lower brine concentration was more than the PPG pack permeability with a higher brine concentration when the PPG pack was not compressed by a piston. However, PPG pack permeability was less when using a lower brine concentration whether the PPG pack was compressed because the PPGs with higher brine concentration loss more water than the PPGs with the lower brine concentrations. According to our paper results the optimum gel pack with a preferred permeability can be designed by the right selection of the gel strength and correct particle size at reservoir pressure

Minimizing Formation Damage for Preformed Particle Gels in Mature Reservoirs

In oilfild operations, it is important to decrease water production and increase the efficiency of oil sweep. A gel treatment is using preformed particle gels (PPGs) to reduce water flow through high-permeability formation in mature reservoirs. The success of PPGs treatment primarily depends on whether or not PPGs can reduce the high permeability zones to the anticipate level. This work sought to find methods that minimized the damage caused by PPGs on unswept, low-permeable zones/areas, thus improving PPG treatment efficiency. These results can help to identify of the best PPG types, particle sizes, and brine concentrations for specific reservoir condition. Both a static filtration test model and load pressure model were used to evaluate the damage caused by various PPGs on sandstone core samples with various degrees of permeability. Two types of particle gels, a strong Daqing gel (DQ) and a weak Liquiblock 40k gel (40K), were used for various experiments, each with a different strength. The particle sizes ranged from 30 to 120 meshes. Sodium chloride (NaCl) was used to prepare all brines. Various brine concentrations at room temperature were selected to prepare the swollen PPGs. The effect of particle size, core permeability, and brine concentration on core damage was investigated. Results of these experiments yielded information useful for promoting the best PPG treatment for conformance control in mature reservoirs. These results can be used to optimize PPG\u27s design and, thus, prevent damage to the unswept, low-permeable zones/areas

Effect of Weak Preformed Particle Gel on Unswept Oil Zones/Areas during Conformance Control Treatments

Preformed particle gel (PPG) has been developed to reduce fluid channels through super-high-permeability streaks/fractures. This was done to decrease water production and improve sweep efficiency for mature oilfields. The success of a PPG treatment depends primarily on whether or not PPG can selectively penetrate into highly permeable channels or fractures while minimizing penetration into lower permeable, unswept zones/areas. The purpose of this work was to determine what factors influence the damage of PPG on low-permeable, unswept zones. A filtration apparatus was designed to determine the possible penetration of PPG into low-permeable sandstone rocks. Filtration curves (the relationship between injection times and filtration volume) were obtained, and the permeability of sandstone cores, both before and after PPG treatment, was measured to determine whether or not PPGs reduce the permeability of low-permeable rocks. A commercial superabsorbent polymer, LiquiBlock 40K gel, was used as a PPG sample for our filtration experiments. LiquiBlock 40K is a weak gel particle with an elastic module of 400 Pa at 0.05% of NaCl (wt%). The particle sizes of the gel ranged from 30 to 120 meshes. Filtration test results showed that 30-120 meshes of LiquiBlock 40K gel did not propagate in the cores with a permeability of \u3c320 mD. This test also indicated that the gel formed a cake on the rock\u27s surface. The damage of particle gel on unswept, low-permeable zones/areas was found to be effectively reduced by controlling both the particle size and the concentration of brine that was used to prepare swollen PPG

Quantitative Analytical Model of the Formation Damage by Gel Particles

Formation damage by gel particles has become one of the most important problems in mature reservoirs. The objective of the quantitative analytical model is to identify an analytical model to the best fit of the preformed particle gels (PPGs) filtration test results. This work will analyze the experiments results of low permeability core samples to evaluate the effect of various brine concentrations and particle sizes. This study used a linear analytical model relationship between cumulative volumes versus filtration time with a good fits result. Linear curve equations for the best fitting equation was obtained. According to quantitative analytical model for all of our filtration tests, the cumulative filtration test volume (Vcf) was explained in this paper. Quantitative analytical model results showed the value of the slop m increases as the injection pressure increases. Compared with the experiments, the results show that, if the value of the intercept b > 2 the damage occurred because the gel particles invasion started into the core surface. Results from the quantitative analytical model were indicated to have a good fitting with almost all of the experimental results. It is the first time to use quantitative analytical model to analysis the formation damage by the PPGs. The results can be used to select the best gel treatment design