This paper discusses the chemical factors that operators must address to successfully substitute seawater for fresh water in borate-crosslinked guar fracturing fluids. Seawater contains cations and anions that affect the performance of the fracturing fluid's components, as well as the fluid's interaction with the formation. Because seawater has high ionic strength, it lowers the viscosity obtained from borate-crosslinked guar. High magnesium in the water consumes hydroxide ions and affects pH control, which in turn affects the equilibrium borate-ion concentration. This paper addresses these problems and provides guidelines for borate fluid formulation to offset seawater characteristics for temperatures as high as 300°F. Borate fluids from seawater can control fluid loss (FL) as well as freshwater borate fluids. Chemical gel breakers for offshore environments have been developed to help control the viscosity reductions in fracturing fluids. Conductivity values with seawater fluids are equal to or better than freshwater fluids. The presence of divalent cations in the seawater fluid caused no harm to the FL properties or the retained conductivity with borate seawater fluids.

Proppant production from hydraulically fractured wells can cause severe operational problems, increase safety concerns, and dramatically reduce economic returns on well-stimulation investments. Methods that have helped eliminate or minimize proppant flowback include modified completion designs, the use of controlled fracture closure for obtaining early closure on the proppant pack, and the use of materials designed to reduce proppant production. Curable resin-coated proppants, chopped fiberglass, thermoplastic strips, and chemicals that modify the surface of the proppant are all accepted methods for minimizing flowback. This paper presents the results of both physical and numerical modeling of proppant flowback recorded during the development of a chemical designed for modifying the proppant surface. The goal of this study was to develop an understanding of the mechanisms that control proppant flowback. Laboratory experiments performed in slot models with no closure stress helped establish the interaction of proppant size, proppant distribution, and fluid velocity. Additional studies of the impact of closure stress, fracture width, and fluid rate on proppant flowback were performed with modified API linear conductivity cells. Data obtained from the physical modeling were used to calibrate a numerical model that predicts proppant flowback. In this model, fluid flow in the proppant pack is described by Darcy's equation for flow through porous media. The resulting velocity distribution allowed local stability to be assessed along the free surface between the proppant pack and the continuous fluid phase. Repeating these steps allowed evaluation of the interface that develops over time.

Reduced production is often caused by local impairment of the formation permeability due to the interaction of the reservoir with drilling and completion fluids. The problem may be further compounded by impairment caused by fines migration during production. High frequency sonic and ultrasonic waves have been used in many industrial applications to remove contaminants like dirt, oil, and grease from parts immersed in fluids. An obvious extension of this application is the removal of wellbore impairment by exposing it to high frequency acoustic waves. The influence of high frequency waves is limited to the near wellbore environment due to high attenuation. Dedicated experiments under realistic downhole conditions have been carried out in both linear as well as radial configurations. We have examined the acoustic power needed to remove near wellbore formation damage due to fines and particles plugging and drilling induced damage. Specific issues related to well completion and envelope of acoustic stimulation are presented. The laboratory results have led to the design and construction of a slim, high power and high frequency (above 10 kHz) downhole acoustic tool for field deployment. This paper outlines the concept and presents key experimental results to support the claim. Key features of a prototype downhole tool are described. Introduction Acoustic waves are traditionally used in the oil industry for exploration and appraisal during seismic and logging surveys. Recently, with the advent of 4D technology, repeated seismic surveys are carried out to monitor the production behavior of a field. Surprisingly, acoustic waves can also be used for production enhancement. The two main potential applications are near wellbore cleaning and enhanced oil recovery. This paper highlights the key development and understanding in the wellbore-cleaning area, specifically, high frequency acoustic stimulation. Formation damage can arise from many well activities during drilling, completion and production. The associated damage mechanisms are numerous. One of the most pervasive mechanisms is the plugging of pores by solid particles. This may be caused by external sources such as drilling mud and drilled solid invasion, or may originate in the porous medium itself, for example when in-situ clay fines are mobilized during production. It is not always possible to prevent formation damage completely, and well stimulation techniques to remove or mitigate the impact of formation damage have been used in the industry since more than half a century ago. Although conventional well stimulation techniques - both matrix and fracturing stimulation - have been applied very successful, they do suffer from some severe limitations. Acoustic cleaning presents a promising new well stimulation technology in the combat against formation damage. It complements the existing stimulation technologies and enlarges the range of options available for cost effective well stimulation. It uses high frequency sound waves to shake loose damaging particles and facilitate their removal by flowing the well. The following discussion substantially enhances and complements that given by Wong et al1. We first outline the motivations and potential applications of acoustic stimulation. Then, experimental data are presented to illustrate cleaning efficiency of acoustic stimulation. Finally, key issues surrounding the design and testing of a prototype downhole tool are expounded. Acoustic stimulation field trials are being planned but details are left to future publications. Conventional Well Stimulation Both matrix stimulation and hydraulic fracture treatments involve the pumping of specialized fluids. Therefore, these techniques are ‘invasive’ and two critical issues immediately become paramount:compatibility between injected fluid and in-situ rock/fluid, tubing and even surface equipment, andfluid placement, diversion and penetration into the rock.

Summary Accurate modeling of an ASP flood requires detailed representation of geochemistry and, if natural acids are present, the saponification process. Geochemistry and saponification affect the propagation of the injected chemicals and the amount of generated natural soaps. These in turn determine the chemical phase behavior and, hence, the effectiveness of the ASP process. In this paper, it is shown that by coupling a multipurpose reservoir simulator (MPRS) with PHREEQC (Parkhurst and Appelo 1999; Charlton and Parkhurst 2008), a robust and flexible tool is developed to model ASP floods. PHREEQC is used as the chemical-reaction engine, which determines the equilibrium state of the chemical processes modeled. The MPRS models the impact of the chemicals on the flow properties, solves the flow equations, and transports the chemicals. The validity of the approach is confirmed by benchmarking the results with the ASP module of the UTCHEM simulator (Delshad et al. 2000). Moreover, ASP corefloods have been matched with the new tool. The functionality of the model also has been tested on a 2D sector model. The advantages of using PHREEQC as the chemical engine include its rich database of chemical species and its flexibility in changing the chemical processes to be modeled. Therefore, the coupling procedure presented in this paper can also be extended to other chemical enhanced-oil-recovery (EOR) methods.

Discussion - No abstract available.