A core based comparison of the reaction characteristics of emulsified and in-situ gelled acids in low permeability, high temperature, gas bearing carbonates

Abstract

A Core Based Comparison Of The Reaction Characteristics Of Emulsified And In-Situ Gelled Acids In Low Permeability, High Temperature, Gas Bearing Carbonates Jack D. Lynn; Jack D. Lynn Saudi Aramco Search for other works by this author on: This Site Google Scholar H.A. Nasr-El-Din H.A. Nasr-El-Din Saudi Aramco Search for other works by this author on: This Site Google Scholar Paper presented at the SPE International Symposium on Oilfield Chemistry, Houston, Texas, February 2001. Paper Number: SPE-65386-MS https://doi.org/10.2118/65386-MS Published: February 13 2001 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Lynn, Jack D., and H.A. Nasr-El-Din. "A Core Based Comparison Of The Reaction Characteristics Of Emulsified And In-Situ Gelled Acids In Low Permeability, High Temperature, Gas Bearing Carbonates." Paper presented at the SPE International Symposium on Oilfield Chemistry, Houston, Texas, February 2001. doi: https://doi.org/10.2118/65386-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference on Oilfield Chemistry Search Advanced Search AbstractThere are a number of acid formulations that will generate deeply penetrating wormholes in carbonate formations. Two of the most recent advances are diesel emulsified acid (DEA) and self-diverting polymer/HCl (in-situ gelled acid, or GA). The acid volumes required for propagation of the wormholes, as well as the characteristics of the wormholes are significantly different in each of these formulations. Two different service company implementations of GA, and one in-house developed DEA formulation were evaluated for stimulation of a high temperature (250°F, 121°C), low permeability Saudi Arabian gas and gas condensate producing carbonate.In this paper, the reaction characteristics of DEA were compared to GA formulations using reservoir condition core floods. The characteristics of the acids that were compared included wormhole propagation rates, volumes of carbonate consumed by the acids, wormhole geometric characteristics, and pressure response during injection. Since the acid formulations called for 28 percent HCl acid concentrations, high temperature stability and corrosion control chemicals of the packages were evaluated.The core study found that the GA formulations enhanced the permeability of core samples significantly more then the emulsified acid. The DEA was the more stable of the acid formulations at 250°F. Both of the GA formulations showed some degree of separation of the corrosion control components at reservoir temperature.The GA was found to require larger volumes of acid to achieve an equivalent penetration distance versus the DEA, and logically, the GA dissolved a larger volume of rock per volume of acid injected. The DEA has a higher rate of wormhole propagation and the DEA leaves no residual material in the generated wormholes. The GA left a residuum of polymeric material in the wormholes even after high rate injection condensate.Iron precipitation was noted on both the core injection and production faces with all of the acids after spending. The two acids types showed individual characteristics that can be applied to acid frac applications, but full understanding of the behavior of each, tested with specific reservoir core is required for a correct acid selection to be made. In specific applications, both acid types can be combined in a multiple stage treatment to result in significant enhancement of acid frac simulations.IntroductionThe K1 and K2 reservoirs are composed of relatively low permeability (0.01 – 10.0 mD) gas/gas condensate bearing carbonates. The temperature of the reservoirs ranges from 250 to 300°F and the produced gas contains up to 5 mol. Percent hydrogen sulfide1. The formations tend to have significant porosity, but low permeability. In other words, the storage capacity of the formations is high, however, their flow capacity is very low. To enhance the productivity of these formations, acid frac stimulation has been selected as the method of choice. This treatment combines a hydraulic fracture stage, with a subsequent acid stimulation to etch the formation face, and allow a wider fracture after closure. As opposed to the traditional fracturing in clastic formations, there is no proppant used in this treatment. The soft nature of carbonate formations would result in embedding of the proppant and significant loss of the conductivity of the fracture on closure. Current technology proscribes the use low-fluid loss, water-gelled fluids to initiate and extend fractures, followed by successive volumes of acid and pad buffers to etch the fracture face2.Fluid loss control has been shown to be a significant factor in the effective propagation and etching of acid induced fractures3,4. To achieve this end, a number of fluid systems have been introduced, including gelled acid5,6, in-situ gelled acids7 and emulsified acids8,9. The present study examines reaction characteristics and propagation patterns of in-situ gelled and emulsified acids in cores obtained from Khuff gas reservoirs. Keywords: injection rate, drilling fluid selection and formulation, core sample, permeability, characteristic, in-situ gelled acid, corrosion inhibitor, drilling fluids and materials, injection, wormhole Subjects: Drilling Fluids and Materials, Formation Evaluation & Management, Drilling fluid selection and formulation (chemistry, properties), Acidizing, Well Operations, Optimization and Stimulation This content is only available via PDF. 2001. Society of Petroleum Engineers You can access this article if you purchase or spend a download.