Preformed particle gel (PPG) has been successfully synthesized and applied to control excess water production in most of the mature, waterflooded oil fields in China. This paper reports on laboratory experiments carried out to investigate PPG transport mechanisms through porous media. Visual observations in etchedglass micromodels demonstrate that PPG propagation through porous media exhibits six patterns of behavior: direct pass, adsorption, deform and pass, snap-off and pass, shrink and pass, and trap. At the macroscopic scale, PPG propagation through porous media can be described by three patterns: pass, broken and pass, and plug. The dominant pattern is determined by the pressure change with time along a tested core (as measured at specific points), the particle-size ratio of injected and produced particles from the core outlet, and the residual resistance factor of each segment along the core. Measurements from micromodel and routine coreflooding experiments show that a swollen PPG particle can pass through a pore throat with a diameter that is smaller than the particle diameter owing to the elasticity and deformability of the swollen PPG particle. The largest diameter ratio of a PPG particle and a pore throat that the PPG particle can pass through depends on the swollen PPG strength. PPG particles can pass through porous media only if the driving pressure gradient is higher than the threshold pressure gradient. The threshold pressure depends on the strength of the swollen PPG and the ratio of the particle diameter and the average pore diameter.

Preformed Particle Gel for Conformance Control: Transport Mechanism Through Porous Media

A comprehensive review of polyacrylamide polymer gels for conformance control

Preformed particle gel (PPG) is a particled superabsorbent crossklinking polymer that can swell up to 200 times its orginal size in brine. The use of PPG as a fluid-diverting agent to control conformance is a novel process designed to overcome some distinct drawbacks inherent in in-situ gelation systems. This paper introduces the effect of gelant compositions and reservoir environments on the two properties of PPG: swollen gel strength and swelling capacity. Results have shown that PPG properties are influenced by gelant compositions, temperature, brine salinity, and pH below 6. Temperature increases PPG swelling capacity but decreases its swollen gel strength. Salinity decreases PPG swelling capacity but increases its swollen gel strength. PPG is thermostable at an elevated temperature of 120°C if a special additive agent is added into its gelant as a composition. PPG is strengthand sizecontrolled, environmentally friendly, and not sensitive to reservoir minerals and formation water salinity. Two field applications are introduced to illustrate the criteria of well candidate selection and the design and operation process of PPG treatments. Field applications show that PPG treatment is a cost-effective method to correct permeability heterogeneity for the reservoirs with fractures or channels, both of which are widely found in mature waterflooded oil fields.

Preformed Particle Gel for Conformance Control: Factors Affecting Its Properties and Applications

Unwanted water production is a serious issue in oiland gas-producing wells. It causes corrosion, scale, and loss of productivity. One method of treating this problem is to chemically reduce unwanted water. This paper discusses the use of polymer systems for this purpose and presents a thorough review of available literature over the last decade. In this paper, field-application data for various polymer systems are summarized over the range of 40 to 150 C (104 to 302 F). These applications cover a wide range of permeabilities from 20 to 2,720 md in sandstone and carbonate reservoirs around the globe. Moreover, the review revealed that the last decade of developments can be categorized into two major types. The first type is polymer gels for total water shutoff in the near-wellbore region, in which a polymer is crosslinked with either an organic or an inorganic crosslinker. The second type is concerned with deep treatment of water-injection wells diverting fluids away from high-permeability zones (thief zones). These thief zones take most of the injected water, which results in a large amount of unrecovered oil. For the total-blocking gels, various systems were identified, such as polyurethane resins, chromium (Cr3þ) crosslinking terpolymers, Cr3þ crosslinking foamed partially hydrolyzed polyacrylamide (PHPA), and nanoparticle polyelectrolyte complexes (PECs) sequestering Cr3þ for elongation of its gelation time with PHPA. In addition, polyethylenimine (PEI) was identified to crosslink various polyacrylamide(PAM-) based polymers. The Petroleos de Venezuela S.A. (PDVSA) Research and Development Center developed a PAM-based thermally stable polymer and an organic crosslinker. The system is applicable for a wide temperature range from 50 to 160 C (130 to 320 F). For the deep modification of water-injection profiles in waterinjection wells, two systems were identified: microspheres prepared from PAM monomers crosslinked with N,N0-methylenebisacrylamide and microspheres produced by crosslinking 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with diacrylamides and methacrylamides of diamines (thermally activated microparticles known as Bright Water). This paper highlights all major developments in these areas.

Polymer Systems for Water Shutoff and Profile Modification: A Review Over the Last Decade

Colloid and interface science is fundamental to many aspects of oil and gas production processes. This review focuses on recent advances in water-based drilling fluids, reservoir fracturing fluids, polymer gels for modifying reservoir permeability, avoiding problems caused by colloidal asphaltene oil fractions and characterising the wettability of reservoir rocks. There have been major advances in the design and responsiveness of polymer and surfactant fluids, in the understanding and control of shale clayrock swelling and in the relationships between mesoscopic-scale phenomena in porous media and reservoir production performance.

Oil and gas production

New Size-Controlled Microgels for Oil Production

In-Depth Permeability Control by Adsorption of Soft Size-Controlled Microgels

Characteristics of Microgels Designed for Water Shutoff and Profile Control

In water shut-off operations, the polymer solution and the crosslinker are currently mixed into surface facilities just before to be injected through the production or injection well and then inside the reservoir. Therefore, the crosslinking system is always subjected to shear stresses while « gelling » and the main question for the operator is the depth of penetration inside the reservoir of the « gelling » system. This paper reports a theoretical and experimental investigation of the process of crosslinking under shear. The model derived from our theoretical analysis predicts that the characteristics which governs penetration in porous media, i.e. viscosity and microgel size, can be easilly calculated from simple shear viscosity measurements. The proposed theory describes the crosslinking under shear as a four successive steps process. By taking into account the break-up of microgels by shear forces as soon as their size reaches a given value, this theory predicts that, under a constant shear rate flow, a solution of monodispersed microgels is obtained at the end of the final step. Using a scaling law approach, we derived a very simple equation linking final viscosity and microgel size to initial polymer characteristics as well as applied shear rate. The final shear stress is expected to be independent of shear rate but proportional to crosslink energy, thus providing a simple way to compare various available crosslinkers. New experimental data, obtained by using a low toxicity crosslinking system, i.e. a weakly hydrolyzed and sulfonated polyacrylamide together with zirconium lactate are reported. All the predictions of our model are in agreement with our own data, as well as with others found in the literature. In addition, new information on the physicochemistry of the acrylate-lactate-zirconium system is obtained. While increasing pH results only in a retardation of the crosslinking process without changing crosslink energy, both a retardation and a weakening of crosslinks is obtained by adding sodium lactate. Injectability experiments in porous media involving the injection of both the polymer and the crosslinker, mixed just at the entrance of the porous medium results in a strong plugging after a given time. On the contrary, the injection of preformed microgel solutions, does not show any plugging tendency, although giving higher mobility reduction in agreement with the proposed theory.

Controlling in-situ gelation of polyacrylamides by zirconium for water shutoff

/pdf/numerical-simulation-of-retention-and-release-of-colloids-in-4flavz0tcv.pdf

Aziz Omari

Papers

New Size-Controlled Microgels for Oil Production

In-Depth Permeability Control by Adsorption of Soft Size-Controlled Microgels

Characteristics of Microgels Designed for Water Shutoff and Profile Control

Controlling in-situ gelation of polyacrylamides by zirconium for water shutoff

Numerical simulation of retention and release of colloids in porous media at the pore scale