Acid Polymer gels having pH less than one have been crosslinked for retarding the chemical and physical activity of hydrochloric acid on calcareous formations. Hydrochloric acid concentrations from & percent to 28 percent have been successfully crosslinked. This new and unique stimulation fluid offers high viscosity with adequate shear stability, perfect support for proppants and clay stabilization. Additionally, the fluid provides effective fluid loss control and retardation of acid reaction enabling live acid to penetrate deeper into the formation for better formation conductivity and practically a residue free break for rapid clean-up of the well after the job. Results of lab and field tests show this new Acid Crosslinked System to be effective stimulation fluid for acidizing and acid fracturing in calcareous and sandstone formations having low formation permeability.

Unlike traditional oilfield biocides, those created using Electro-Chemical Activation (ECA) technology, do not interference with gel breakers, do not increase TDS levels, leave no residual toxic chemicals, are cost competitive and are extremely effective killing bacteria without the microorganisms becoming resistant to the natural biocide solutions. This paper discusses

A significant application of multiple tracers is their use in tracing different proppant concentration stages and/or types of proppant to determine their effective wellbore distribution at the fracture entrance. Extensive fracture intervals heterogeneous formations with large containing multiple perforated intervals or hydraulic fracture treatments that utilize the limited entry technique provide one of the best opportunities for using multiple tracers to evaluate proppant distribution. Historically, single isotope tracers (usually Iridium baked or painted onto frac sand) and conventional gamma ray - temperature logs were employed to ascertain fluid and/or propped fracture the wellbore. height at Deviated wellbores or fractures whose azimuth was not vertical caused this analysis technique to yield a lower boundary on fracture height since the full extent of the induced fracture may occur outside the depth of investigation of the scintillation tool being used. Over the last several years, the use of multiple gamma ray tracers in conjunction with advanced gamma ray spectroscopy logging methods has undergone significant evolution and improvement. One of the principal advances is software to differentiate up to four isotopes and their presence inside or outside the wellbore. Much research has been devoted to the development of radioactive particles which exhibit insignificant tracer wash off and offer superior representation of the transport and placement of the medium they are intended to trace. With the single tracer, after-frac gamma ray log approach, if some or most of the radioactive material It washes off of the tagged proppant and becomes dissolved in the fracturing fluid, there was little reason to despair. With the recent advances in gamma spectroscopy tracer logging where both particle and soluble tracers are injected simultaneously with the intent of, differentiating fluid and proppant placement and distribution, this washoff of radioactive material from the tagged proppant has become the subject of great concern. Certainly, the discrimination of propped and induced fracture height becomes impossible if this washoff is significant. Today, proppant tracers are currently available which exhibit absolutely no radioactive washoff and have virtually the same particle size, density, and crush resistance as the proppants. For the application of studying proppant distribution, superior tracers and advanced gamma spectroscopy logging methods are both needed and required.

A significant application of multiple tracers is their use in tracing different proppant concentration stages and/or types of proppant to determine their effective wellbore distribution at the fracture entrance. Extensive fracture intervals heterogeneous formations with large containing multiple perforated intervals or hydraulic fracture treatments that utilize the limited entry technique provide one of the best opportunities for using multiple tracers to evaluate proppant distribution.

Surfactants have performed well in a variety of applications with regard to stimulation. The role of surfactants, or surface active agents, in both acidizing and fracturing has been somewhat taken for granted; but these agents nonetheless play an extremely important and ever-increasing part in almost all successful stimulation treatments. Surfactants have been discussed thoroughly in the literature with respect to use in oil well treating fluids. Until recently, most surfactants used in stimulation have come from one of two families. The most commonly used are hydrocarbon-based, and the others consist of silicone-based materials. Numerous blends of these types are used to deal with a number of situations. In varying concentrations, the above-mentioned "conventional" surfactants have been used in a variety of applications which are as follows. 1. To lower the surface tension or interfacial tension of a fluid. 2. To provide non-emulsion characteristics to a fluid. 3. To provide emulsion-breaking characteristics to a fluid. 4. To provide emulsion-forming characteristics to a fluid. 5. To provide foaming characteristics to a fluid. 6. To suspend fines or particles in fluids. 7. To retard or extend the reaction time of various acids. 8. To allow more effective penetration by aqueous or acid systems. 9. To facilitate a desired wetting function on a particular surface (i.e., metal, rock, etc.). 10. To assist or prevent various types of material in adsorbing to particular surfaces under certain conditions or to allow low adsorption. 11. To provide protection from various harmful reactions (i.e., corrosion, precipitation, etc.).4 12. To allow interaction with other physical problems in the oil or gas reservoir such as fluid imbibitions, capillarity, saturation or permeability.5"6 13. To allow water block removal or more effective treatment load recovery. 14. To improve wetting and thereby hydration of polymers used in stimulation. There are probably other uses which could be mentioned, but those above are generally considered most essential. Correct use requires careful selection of a particular surfactant type. The criteria for surfactant selection for use in a treatment is given below to emphasize the importance of appropriate materials.

Foamed stimulation has been broadened to include the use of high- and low-quality (30% to 75% nitrogen) foams for acidizing soluble formations. To insure correct placement of foamed acidizing systems, foamed diverting techniques using high-quality (80% to 90% nitrogen) foamed water systems are currentIy being employed in several West Texas and Southeast New Mexico areas. Application of these techniques has been successful in both producing and injection wells. The mechanics of these systems will be discussed along with comparative results and current cost economics.

Using spectral gamma ray imaging to identify issues of fracture stimulation placement has been well documented and enhanced by providing methods to interpret inside or near wellbore phenomena as well as fracturing phenomena occurring within 25 inches of the wellbore. Recent studies by Robinson and Voneiff have confirmed that in most vertical or near vertical wells, fracture heights determined by tracers are equivalent to or within ten percent of fracture heights predicted by 3D models or post-fracture treatment performance testing. " Furthermore, it has been determined that when tracers are proportioned properly throughout proppant slurries and carried as an integral part of non-washing, non-crushing, non-abrasion loss carriers, the counts as determined by spectral gamma ray imaging are directly related to fracture width.* This has successfully been corroborated by correlations made using long-spaced or dipole sonic logging and refined by an algorithm developed to quantify fracture width at the wellbore. Most recently a case study has shown that tracers may be used to confirm that fracture closure may not occur as quickly as is often calculated or assumed.