Philip D. Nguyen

Fracture-Related Diagenesis May Impact Conductivity

Rapid loss of fracture conductivity after hydraulic fracture stimulation has often been attributed to the migration of formation fines into the proppant pack or the generation of fines derived from proppant crushing. Generation of crystalline and amorphous porosity-filling minerals can occur within the proppant pack because of chemical compositional differences between the proppant and the formation, and the compaction of the proppant bed because of proppant pressure solution reactions. Findings presented in this paper suggest that diagenesis-type reactions that can occur between proppant and freshly fractured rock surfaces can lead to rapid loss of proppant-pack porosity and loss of conductivity.

Foaming Aqueous-Based Curable Treatment Fluids Enhances Placement and Consolidation Performance

Conventional solvent-based resins (SBRs) have often been used to resolve solids-production problems in producing wells by coating the particulates, such as formation sand, fines, and proppant, with a curable resin to hold the grains together without reducing the treated pack’s permeability. However, the SBRs have low flashpoints that can present safety issues during storage, handling, and well-completion operations. These resin systems have been typically applied in short intervals of less than 30 ft and have had limited success in longer intervals. With the recent development and applications of aqueous-based resins (ABRs), these drawbacks have been overcome. Because solvent-based chemicals are replaced with aqueous brines as carriers in treatment fluids, ABRs have high flashpoints, similar to those of water. Additionally, because ABRs are aqueousbased fluids, they can be foamed so that the operator may simply bullhead the fluid directly into the wellbore to treat long intervals without requiring a rig or zone isolation packers. This paper presents the results of laboratory experiments aimed at understanding and quantifying the performance of ABR treatment fluids in consolidating weakly or unconsolidated formation sands or loose proppant packs. Consolidation strengths and scanning electron micrographs of the treated formation sand or proppant packs were analyzed to identify the mechanisms behind the treatment fluids in providing cohesion between particulates and how the pore channels within a pack matrix remain open, minimizing permeability loss. Both foamed and nonfoamed ABRs were determined to provide effective consolidation levels to the treated formation sandpacks, regardless of whether foamed or not, aqueous post-flush fluid was applied. However, only foamed ABRs allowed resin to remain on the proppant after the treated pack was overdisplaced with nitrogen gas or a nonaqueous fluid, resulting in high consolidation strength and retained permeability. Foaming ABRs enhances the effectiveness of their placement into formation intervals by providing an effective means for diversion and better coverage, and extending treatment-fluid volume. When applied using bullheading or coiled tubing, potential applications of ABR systems include primary or remedial treatments of weakly or unconsolidated formations for sand control or fines stabilization and remedial treatments of propped fractures for proppant-flowback control.

Gravel Pack Designs of Highly-Deviated Wells with an Alternative Flow-Path Concept

Alpha-Beta gravel packing procedures have been used with a moderate degree of success in highly -deviated wells. Incorrect concentrations of gravel and/or pump rates can result in bridge formation in the open hole/screen annulus and Beta wave initiation prior to reaching the toe. If there is a high leakoff zone, gravel concentration will increase, and there may be insufficient velocity to trans port the solids farther down the well. Either factor or a combination of the two can lead to formation of a bridge in the openhole/screen annulus and an early initiation of the Beta wave. Other effects that could lead to bridge formation include: flow restriction and blockage from collapse of an unstable open hole section, and changes in annular velocity transition from one hole size to another. Incomplete gravel placement and the presence of voids around the screen can result from all of the complications described above. To overcome these, an alternative flow path system has been developed. If a bridge forms, the alternative path allows the slurry to bypass it. A number of physical models have been used to design and examine the effectiveness of the system, which has been validated in field applications. A numerical model has also been developed to assist with the gravel pack designs in highly-deviated wells. The model simulates the alternative flow -path concept as well as conventional gravel packing in open hole or cased -hole completions of arbitrary deviation. Details of the alt ernative flow -path scheme as well as the formulation of the numerical model are presented in this paper. Simulation results were compared to observations in the physical models.

Maximizing Well Productivity Through Water and Sand Management - A Combined Treatment

Production of large volumes of water, coupled with production of formation sand and fines from oil and gas wells, often curtails the potential production of hydrocarbon. It is therefore highly desirable to decrease the volume of water and mitigate the solids produced from producing wells. Water and sand control generally have been addressed as separate problems with different treatment solutions. This paper discusses the development, and presents the field testing results, of a 2-step process that combines both water- and sand-control treatments into a single treatment. Laboratory experiments were performed to examine the impact of these combined treatments. The relative permeability modifier (RPM) treatment results in water permeability reduction with little or no reduction in permeability to oil. Treatment with a consolidating agent transforms the unconsolidated formation sand and/or loosely packed proppant into a cohesive, consolidated, yet highly permeable, pack. The combined process has been field tested successfully. Results from field tests have shown that this process helped reduce on average 50% of water production, effectively eliminated the production of formation sand, and allowed the wells to withstand high production flow rates.

Remediation of Proppant Flowback-Laboratory and Field Studies

This paper presents the results of laboratory studies and field case histories of a remedial treatment technique using a lowviscosity consolidation fluid system that is placed into the propped fractures by coiled tubing (CT) or jointed pipe coupled with a pressure pulsing tool. The treatment fluids are designed to provide consolidation (for previously placed proppant) near the wellbore to glue the proppant grains in place without damaging the permeability of the proppant pack. Laboratory flow testing indicates that the proppant pack in a fracture model under closure stress only requires lowstrength bonds between proppant grains to withstand high production flow rates. The consolidation treatment transforms the loosely packed proppant in the fractures and the formation sand close to the wellbore into a cohesive, consolidated, yet highly permeable pack. Field case histories are presented and the treatment procedures, precautions, and recommendations for implementing the treatment process are discussed. One major advantage of this remedial treatment method is the ability to place the treatment fluid into the propped fractures, regardless of the number of perforation intervals and the length of the perforated intervals without mechanical isolation between the intervals. The fluid placement efficiency of this process makes remediation economically feasible, especially in wells with marginal reserves.