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Results
Abstract Kaolinite migration is a common but often well treated formation damage mechanism. Undesired secondary reactions leading to precipitates and/or limited treatment coverage related to the presence of additional damage mechanisms are common issues. The present work documents a field case study of kaolinite damage control that included dissolution and stabilization under a very unfavorable environment in which CaCO3 scales and asphaltenes also co-existed. The case herein described is the last development stage after several unsuccessful trials in the same area which included the injection of conventional mud acid and retarded HF sandstone type systems. A new chemistry approach incorporating retarded flouboric acid generation and high performance chelants for metallic ions control was developed. Also key, was realizing fines wettability to oil (through critical rate tests to both water and oil) which allowed including proper pre-flushes on final treatment deployment. Along with a summary of the fines problem description in the area of interest, laboratory protocols, stimulation design approach and field trial results are presented. According to treated well results, up to 50% PI improvement could be now attained in ~60% of total well count where same damage configuration is expected to be present.
- Europe (0.94)
- North America > United States > Louisiana (0.47)
- North America > United States > California > San Francisco County > San Francisco (0.28)
- Geology > Mineral > Silicate > Phyllosilicate (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.67)
- South America > Colombia > Barco Formation (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Statfjord Group (0.99)
- Europe > Norway > North Sea > Northern North Sea > East Shetland Basin > PL 050 > Block 34/10 > Gullfaks Field > Lunde Formation (0.99)
- (3 more...)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (0.93)
Abstract Mud acid, which is composed of HCl and HF, is commonly used to remove the formation damage in sandstone reservoirs. However, many problems are associated with HCl acid, especially at high temperatures. In this study, formic acid was used to remove carbonate minerals as a preflush and with the main HF stage. A series of formic acid and HF mixtures with different ratios and concentrations were tested. Sandstone cores featured by different minerologies with dimensions of 1.5 in. x 6 in. were used in the coreflood experiments, which were run at a flow rate of 5 cm/min and temperatures from 77 to 350°F. The cores were analyzed by CT scan before and after the acidizing to investigate the effect of the acid. The core effluent samples were analyzed to determine concentrations of Ca, Mg, Fe, Si, and Al by ICP. F NMR was utilized to follow the reaction kinetics and products. Zeta potentials of clay particles (kaolinite, illite, and chlorite) were measured in various acid solutions Formic acid (9 wt%) damaged sandstone cores. Zeta potential measurements indicated that formic acid can trigger fines flocculation. Addition of 5 wt% ammonium chloride helps to shield negative charges on clay surface. Analysis of core effluent samples indicated that there was CaF2 precipitate in the core when a small volume of preflush was used. Coreflood tests highlighted that formic acid/HF caused loss of core permeability. This paper will discuss the detailed chemical reactions occurred within cores and were followed by chemical analysis of core effluent samples and F NMR. Secondary reaction between clay minerals and HF became faster at higher temperature, and decreased the ratio of Si/Al. It was also found that different clay minerals react with HF offering very different concentrations of Al and Si in spent acid.
- North America > United States > Texas (0.47)
- North America > United States > Louisiana (0.28)
- Asia > Middle East > Saudi Arabia (0.28)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Silicate (1.00)
Abstract Effective removal of drilling-mud filter cake during well completion is essential to reduce the formation damage caused by drilling activities in many production and injection wells. This task is very difficult to achieve, especially in horizontal/multilateral wells. Harsh chemical treatments (acids, oxidizers, and chelating agents) have been used extensively to conduct water-based mudcake cleanup treatments. However, these approaches have been limited due to the associated high corrosion rates and un-even mudcake removal. With their controlled reaction with the mudcake, mild chemical nature, better health, safety and environmental (HSE) profile, different acid-precursor systems provide an excellent alternative to harsh chemical treatments in high temperature formations. This work examines the efficiency of two acid-precursor systems to be used for mudcake removal in horizontal wells. These two acid-precursors (an ester of acetic and formic acid) will generate acid at slow rate at downhole conditions, resulting in uniform mudcake removal. The acid release rate of both in-situ acid generator systems was calculated at targeted average reservoir bottom-hole temperature of 130°F. The study was conducted at simulated reservoir conditions of 500 psi pressure for building the filter cake and 300 psi pressure for soaking the treatment. Drill-in fluids (DIF) sample collected from the field was used for conducting the filter cake removal tests. Return permeability experiments were performed using HPHT filter press cell. Filter cake removal efficiency of formate ester showed that this system removed 59.3 wt% water-based mudcake formed on a 5 μm ceramic disk when soaked for a prescribed period of 24 hours at 130°F and 300 psi nitrogen pressure. Similarly, filter cake removal efficiency of acetate ester tested on similar conditions removed 30.4 wt% of the filter cake. The break through time for the reactive fluid to penetrate through the mud filter cake was found to be approximately 15 hours for formate ester. Acetate aster system breakthrough was found to be nearly 7 days. Compared to acidic brine (1 wt% HCl), these systems will have slower fluid loss rates where the amounts of collected filtrate were found to be 14.6, 2.7, and 2.5 cm for 1 wt% HCl, formate ester and acetate ester, respectively, after soaking time of 2 hours.
- North America > United States (1.00)
- Europe (1.00)
- Asia > Middle East > Saudi Arabia (0.47)
Abstract Acid-in-diesel emulsified acid has been used in the oilfield for many years. Emulsified acid systems are retarded systems that can be used effectively in stimulation of carbonate reservoirs. Emulsified acids have primarily been used in acid fracturing and matrix acidizing. The delayed nature of emulsified acids is useful in generating longer etched fractures or deeper wormholes. To predict the penetration depth of wormholes or the length obtained from an acid fracturing treatment, diffusion coefficient values need to be estimated. This paper discusses the rheology, and reaction kinetics of emulsified acids formulated using a new emulsifier. The emulsified acid systems were prepared at 15 wt% HCl and 0.7 acid volume fraction. Emulsifier concentration was varied from 0.5 to 2.0 vol%. For all emulsions, viscosity was measured using an HPHT rheometer. Emulsified acid reaction rates, and hence acid diffusivity, were measured using a rotating disk apparatus at a temperature of 230 °F. Disk rotational speeds were varied from 100 to 1,500 rev/min. Samples of the reacted acid, from the reactor, were collected and analyzed using the Inductively Coupled Plasma, to measure calcium and magnesium concentrations. Rheological measurements indicated that emulsified acid systems behaved as a non-Newtonian shear-thinning fluid, and this behavior can be represented by a power law model. The emulsifier concentration and temperature affect greatly the viscosity of emulsified acids. The new emulsified acid systems achieved low reaction and diffusion rates; as the emulsifier concentration increased, both reaction and diffusion rates decreased. Emulsified acid –dolomite reaction was mass transfer limited at low emulsifier concentration. The behavior was in the middle region between mass transfer limited and surface reaction limited for higher emulsifier concentrations. At high emulsifier concentration, the reaction appears to be surface reaction limited. These results can be used to optimize the design of carbonate acidizing treatments using emulsified acid.
- Geology > Mineral (0.95)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.78)
Abstract Different organic-HF acid mixtures have been used to stimulate sandstone formations. Typically, they are used as alternative to regular mud acid in order to overcome its potential limitations such as rapid spending, high corrosion rate and incompatibility with sensitive clays. However, organic-HF systems are more susceptible to fluoride-based precipitations because they contain high amount of free fluoride ions. This paper focuses on identifying the type of precipitations that occur during reactions of organic-HF acids, and on determining the factors that affect these precipitations. Solutions of different organic-HF acids namely formic, acetic and citric acid, containing HF concentrations of 0.5, 1 and 1.5 wt%, were examined in this study. Aluminum chloride or iron chloride were added separately to each organic-HF acid solution to contain 1,000; 5,000 or 10,000 mg/L of aluminum or iron (III) ions, respectively. The acid mixtures were neutralized by adding sodium hydroxide. Filtered solutions were analyzed using inductively coupled plasma (ICP) to assess the ability of used acids to hold Al and Fe (III) dissolved ions, while formed solid precipitates were analyzed by X-ray diffraction (XRD). The type and amount of precipitates were found to be mainly dependent on solution pH, organic-HF type, and initial free fluoride concentration. All live organic-HF acids containing dissolved iron (III) showed no precipitation even after iron (III) level reached 10,000 mg/L. However, when solution pH value was raised, none of tested organic-HF acids were able to prevent iron fluoride precipitation. On the other hand, the main factor that controlled the aluminum-fluoride precipitation was found to be F/Al ratio. It was found that there is a critical F/Al ratio, above which the aluminum fluoride precipitation occurred.
- Asia > Middle East > Saudi Arabia (0.46)
- North America > United States > Louisiana (0.28)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Mineral > Halide (1.00)
Effective Matrix Stimulation of High-Temperature Carbonate Formations in South Sumatra Through the Combination of Emulsified and Viscoelastic Self- Diverting Acids
Madyanova, M. (Schlumberger) | Hezmela, R. (Schlumberger) | Artola, P. (Schlumberger) | Guimaraes, C. R. (Schlumberger) | Iriyanto, B. (Talisman Jambi Merang )
Abstract The biggest challenges for successful matrix acidizing treatments on carbonate formations are the creation of an effective network of wormholes and obtaining uniform coverage. Typical matrix treatments often require low injection rates, and therefore hydrochloric acid cannot be used alone because rapid acid spending severely limits the acid penetrationat elevated temperatures. This high reaction rate causes face dissolution, fails to create a wormhole network long enough to effectively bypass the damaged zone around the wellbore that leads to the creation of dominating wormhole. The Sungai Kenawang (SKN) onshore gas-condensate field, located at the southwest part of the Jambi Merang block in the South Sumatera Province, is a carbonate buildup, which is part of an isolated bank containing a group of buildups. The Baturaja formation, located at depths around 7,000 ft, is a thick gas condensate reservoir with permeabilities in the range of 10 to 350 mD, bottomhole temperatures range of 280 °F and 350 °F and the presence of H2S. The standard method used to stimulate these carbonates was pumping 15% gelled hydrochloric acid through coiled tubing. Production logs and pressure build-up analysis have shown positive skin values post stimulation and that the production was mainly coming from the upper zones, with minimal contribution from the lower zones. This paper describes the application of a high temperature, highly retarded emulsified acid system that slows the reaction times by a factor of 5 to 15 compared to conventional HCl systems. The emulsified acid system combined with a selfdiverting viscoelastic surfactant based acid was able to achieve complete stimulation of a 197 ft long perforated interval without the need of coiled tubing. A pressure buid-up test showed a post-stimulation skin value of – 3.3 and the production log analysis demonstrated complete and uniform zonal coverage with the upper zones contributing with 53% of the total well production and the lower zone with 47%.
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.69)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.68)
- Asia > Indonesia > Sumatra > South Sumatra > Sungai Kenawang Field (0.99)
- Asia > Indonesia > Sumatra > South Sumatra > South Sumatra Basin > Muara Enim Formation (0.99)
- Well Completion > Completion Installation and Operations > Perforating (1.00)
- Well Completion > Acidizing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Gas-condensate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)