Experimental Investigation of Particulate Polylactic Acid Diversion in Matrix Acidizing

Abstract

Polylactic Acid (PLA) is increasingly used in the oil industry and specifically for diversion in matrix acidizing as evidenced by a number of field cases recently published. The solid polyester is particularly attractive due to its ability to degrade in the presence of water and heat, negating the need for cleanup fluids or complicated procedures. A majority of the analysis on the effectiveness of PLA thus far comprises experiments on artificially created slots, filter cake analysis, and field trials. This paper demonstrates the effect of PLA in wormholes developed by acidizing outcrop cores. In these experiments, a wormhole is generated in a portion of the core by limiting the amount of acid injected. Next, the PLA is injected into the core using a heavy brine suspension. Finally, more acid is injected until a wormhole breaks through the core. Computer Tomography (CT) scans are taken, and the pressure drop across the core is recorded at each stage. Experiments were conducted for a variety of initial wormhole lengths. It can be difficult to suspend PLA while injecting it through a core in a way that is benign to the core, acid, and PLA; and in a way that does not add any pressure drop or diversion due to viscosity changes. This paper describes and justifies a suitable method of keeping PLA suspended to allow its use in core flood experiments. The CT scans show that even when the PLA plugs the wormhole, additional acid tends to continue to develop the dominant wormhole. The pressure drop profiles show that the pressure drop due to PLA injection is proportional to the mass of PLA, both in the wormhole and on the core surface. The pressure profiles also show that there is an increased pressure drop due to PLA in the wormhole versus in a filter cake on the surface. This paper details a new method of visualizing and analyzing the effect of PLA in a multistage acidizing treatment. Empirical correlations are presented for estimating the pressure drop caused by PLA, both as a filter cake on the formation surface and as a filling inside wormholes. The correlations were incorporated in a comprehensive carbonate acidizing model to predict the diversion efficiency of PLA particles. The simulation is verified using published field trials of diversion treatments.

Coreflood Testing of Gas-Blocking Agents: Selectivity in High-Heterogeneity Reservoirs and Efficiency in Low-Temperature Conditions

“…For further profitable field development, the selective gas isolation of high-permeability zones is required. However, implementation of gas-blocking technologies is difficult due to the length requirement of producing horizontal wells being up to 2000 m and “fishbone” wells’ branching. , …”

“…There are several mechanical and chemical gas-blocking methods . Mechanical materials in the long horizontal well, such as bridge plugs and packers, can be difficult to operate and require iterations of operations since it is difficult to determine the exact intervals of gas breakthrough . Mechanical gas-blocking methods require long-term shutdown of wells, which may entail additional economic risks since production is carried out in natural mode using only production wells.…”

“…However, implementation of gas-blocking technologies is difficult due to the length requirement of producing horizontal wells being up to 2000 m and "fishbone" wells' branching. 1,2 There are several mechanical and chemical gas-blocking methods. 1 Mechanical materials in the long horizontal well, such as bridge plugs and packers, can be difficult to operate and require iterations of operations since it is difficult to determine the exact intervals of gas breakthrough.…”

Influence of Geological and Technological Parameters on Effectiveness of Hydrochloric Acid Treatment of Carbonate Reservoirs

“…To enhance the effectiveness of the hydrochloric acid effect on reservoir, a large number of modifications of acid compositions (AC) are being currently developed, contributing to the individual nature of the process of the treatment of productive sediments near wellbore [7][8][9]. To exercise a competent approach to the design of hydrochloric acid treatment, physical and chemical properties of formation fluids, lithologic and mineralogical composition, type of rock paleolithic facies and pressure-temperature conditions will be taken into account [10].…”