Stimulation of carbonate reservoirs using suitable acid systems is common practice to alleviate damage caused by the drilling and completion operations and to increase permeability by way of acid fracturing operations in tight formations. This process creates conductive channels in the pay zone allowing for oil and gas recovery. Several drawbacks however can be encountered, particularly at elevated temperatures, when using strong mineral acids, i.e., hydrochloric acid (HCl). Under these harsh conditions, propagation of live acid deep into the formation is hindered by unfavorable reaction kinetics between the acid and rock matrix. To address some of these challenges, the industry moved towards emulsifying the mineral acid in a hydrocarbon phase, i.e., diesel. The advantages to this strategy are two-fold, i.e., it provides a temporary barrier between the acid and the formation and offers some degree of corrosion protection for the metal tubulars during the pumping stage. The two main drawbacks are high friction losses and cumbersome mixing requirements that create complexity and impose quality control challenges in the field. To address some of these challenges, we recently reported on the design and characterization of a new acidizing platform consisting of a suite of low-viscosity acid systems (LVAS) having the desired retardation profile for acid stimulation under harsh reservoir conditions. To better design acid stimulation treatments in the field, it is imperative to gain a deeper understanding of the reaction kinetics between the fluid and rock matrix, specifically the reaction rate constant and diffusion coefficient. In this paper, a comprehensive kinetics study was conducted for an LVAS formulation. This previously reported system is comprised of a pre-engineered blend of strong organic and mineral acids. This study was performed at 3000 psi, across a wide temperature range (180-350°F) and disk rotational speeds (250 up to 1000 rpm) using a custom designed rotating disk apparatus. Homogenous calcite disk samples were cut in 1.0" thickness and 1.5" diameter. The mineralogy and homogeneity of the core samples were characterized using powder X-ray diffraction (PXRD). The reaction rate constant for the Newtonian hybrid acid system was measured at 300°F and 500 rpm and determined to be 3.3×10−6 gmole/cm2.s. The performance of this fluid system was benchmarked to a previously reported weak organic acid system (i.e., 20 wt% glutamic Di-acetic acid [GLDA]). Notably, LVAS was able to control the calcite/rock reaction on a magnitude comparable to 20 wt% GLDA. In addition, the diffusion coefficient for LVAS was found to be similar to that of 15 wt% HCl-based emulsified acid systems. The LVAS allows faster batch mixing compared to emulsified acid, achieving low viscosity and manageable corrosion. The measured reaction parameters and the calculated activation energy for LVAS was higher than that of other acid systems indicating the ability of LVAS to control the reaction with calcite rocks. The LVAS presents advantageous performing qualities enhancing conductivity in the rock and porous matrix.
Resin coated proppants are widely used in fracturing applications. They serve two purposes namely to increase the strength of proppant material to withstand closure stresses and to mitigate any proppant flowback. Typically, resins used for proppant coatings are made up of hydrophobic polymers and are inherently incompatible with the aqueous fracturing fluid. To avoid any slugging issues due to this incompatibility, the coated resins are typically semi-cured. The coating process needs to be undertaken during proppant manufacturing and adds to the overall cost of the proppants used. In this paper we showcase the development of novel insitu generated hybrid materials that enhance the proppant strength. Moreover, the resins used for proppant coating are introduced as a water external emulsion, thus making them compatible with the aqueous fracturing fluids. We show that by using a solid resin based emulsion system as proppant coating material we could introduce this system on-the-fly along with the fracturing fluid without facing any incompatibility issues between the hydrophobic resin and the aqueous fracturing fluid. We further show that by using tactoid based filler materials suspended with the emulsified resin we could tremendously enhance the overall mechanical strength of the proppants. The solid resin above the temperatures of 60°C melts and starts to intercalate into the layered tactoid fillers. The process of intercalation is driven by mechanical shear as the fracturing fluid is pumped downhole, as well as by thermodynamics of intercalation. Specific structural modifications were utilized to increase the entropy of the layered tactoids, facilitating the intercalation of resin. Increased intercalation of the resin inside confined spaces of the tactoid overcame the Van der Waals forces that hold the tactoid layers together. As the tactoid layers separated they formed an exfoliated structure of high aspect ratio filler with nanoscale dimensions of around 1nm thickness. The high aspect ratio nanofillers uniformly dispersed in the resin matrix ensured effective load transfer from the matrix thereby tremendous increase in the overall mechanical strength of the resin coated proppants. We studied the mechanical properties by evaluating the compression strength of the resin nanocomposite coated proppants in comparison with the pristine resin coated and uncoated proppants. The mechanical strength enhancements in the nanocomposite coated proppants were clearly evident from this study. Structural evaluation of nanocomposites showed uniform dispersion of the fillers in epoxy matrix could be achieved whilst generating the nanofillers insitu. The viscoelastic properties of the nanocomposite based coating were also investigated and showed better mechanical behavior over those of pristine resin coatings. Novelty of this paper of newly developed proppant coating nanocomposite material is in situ generation of the nano fillers and on the fly deployment of the resin coating material along with fracturing fluid due to enhanced compatibility.
Reservoir stimulation is a widely used technique in the oil and gas industry for increasing the productivity of hydrocarbon reservoirs, most notably in carbonate formations. This work aims to develop an optimization workflow under uncertainty for matrix acidizing. A reactive transport model is implemented in a finite-element framework to simulate the initiation and propagation of dissolution channels in porous carbonate rock. The model is verified using an analytical solution. We utilize surrogate modeling based on polynomial chaos expansion (PCE) and Sobol indices to identify the most significant parameters. We investigate the effect of varying 12 identified parameters on the efficiency of the stimulation process using dimensionless groups, including the Damkoḧler, Peclet, and acid capacity numbers. Furthermore, the surrogate model reproduces the physics-based results accurately, including the dissolution channels, the pore volume to breakthrough, and the effective permeability of the stimulated rock. The developed workflow assesses how uncertainties propagate to the model's response, where the surrogate model is used to calculate the univariate effect. The global sensitivity analysis shows that the acid capacity number is the most significant parameter for the pore volume to breakthrough with the highest Sobol index. The marginal effect calculated for the individual parameter confirms the results from Sobol indices. This work provides a systematic workflow for uncertainty analysis and optimization applied to the processes of rock stimulation. Characterizing the impact of uncertainty provides physical insights and a better understanding of the matrix acidizing process.
Acid fracturing has been an integral part of reservoir development strategies for carbonate reservoirs as mechanical and chemical means of bypassing formation damage enhances productivity. Over the past few years, acid fracturing has significantly increased targeting more carbonate reservoirs. There is a need to fully address the heterogeneous petrophysical and geomechanical properties of target reservoirs, which adversely affects the stimulation efficiency and production if fluids are not properly designed. When injecting stimulation fluids to fracture the reservoir rock, the fluid is prone to traveling along the path of least resistance, and consequently less permeable zones and high stress reservoir rock receive treatments that could be further improved or enhanced. Accordingly, this drives the industry to continuously develop high performance chemical dynamic diverter systems. To ensure an effective and sufficient acid fracturing is achieved when treating long intervals of perforated clusters or openhole horizontal wells. Recent advancements in diversion technology utilize various forms of degradable particles, where they serve to provide a temporary bridge, which is either inside the existing fracture or the perforation entrance. This allows for intentionally forming a low permeability pack, allowing the pressure inside the fracture to increase and redirect the next stage of fluid to the zone having a higher degree of stress that has not yet been covered by the fracture. The objective is to increase the fracture complexity, particularly in vertical wells where there is big variation in geomechanical properties of the formation. To gain a deeper understanding of the performance of these diverters, a simulation study was conducted to analyze and compare the efficiency of particulate diverters used in two pilot wells. Fracture modelling and sensitivity analysis were also performed to understand the effect of diverters on the fracture geometry. To match the actual treatments, modelling validation and control were achieved through utilization of field data such as production logging, temperature surveys and pressure buildup tests. The study determined that the success of the particulate diverter employed for the fracturing application is heavily dependent and governed by the geomechanical properties of the treated zone and the ability of the diverter to overcome the stress difference in the stimulated interval. Optimization of the diverter design and degradation profile is still needed to improve and achieve the best stimulation efficiency.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.