Acid Fracturing Technique for Carbonate Reservoirs Using Nitric Acid Powder
Bibliographic record
Abstract
Abstract The length of the etched fracture is rather limited utilizing traditional acid fracturing techniques, especially in a high-temperature carbonate reservoir. Although the propped fractures may have a deeper penetration, they have such drawbacks as low fracture conductivity, unintended proppant bridging, and subsequent proppant flow back. This paper presents the development of a new acid fracturing technique, Nitric Acid Powder (NAP) acid fracturing, to improve the acid penetration and fracture conductivity. The NAP acid fracturing technique has been applied in several oil fields in China. It has been shown that the NAP acid fracturing technique has the advantages of both hydraulic fracturing and acid fracturing, such as long effective penetration, high fracture conductivity, low cost, and easy field operation. We have developed a comprehensive mathematical model for the NAP acid fracturing technique to facilitate the optimization of the field treatment design. The model presented considers fracture growth, acid transport and reaction, leak-off, etched width of the fracture, and so on. The study has shown that the NAP acid fracturing technique could reach a very high stimulation ratio, even in a high-temperature carbonate reservoir. Therefore, it is an innovative and promising technique for well stimulation in carbonate reservoirs. Introduction Carbonate formations generally have a low permeability and can be highly fissured. Long fractures in acid fracturing treatments are essential to maximize production. Acid must react with the walls of the fracture to form a channel that remains open after the treatment. Flow channels can be formed as a result of an uneven reaction with the rock surface or preferential reaction with minerals heterogeneously distributed in the formation. If the formation temperature is very high, the reaction rate will be fast. If this occurs, the acid treatment will tend to remain in the near wellbore vicinity, resulting in short penetration. Acid fracturing techniques are the primary preference in carbonate formations. Operationally, acid fracturing is less complicated because no propping agents are used, which eliminates the risk of a screen-out and subsequent problems of proppant flowback and cleanout from the wellbore. Generally, acid-etched fractures have high conductivity, although they are quite limited in penetration, whereas the propped fractures have limited conductivity with deeper fracture penetration. The techniques to overcome the limitations of conductivity and penetration for the carbonate formation have been studied continuously to enhance the acid fracturing technology. Equilibrium acid fracturing was developed by Tinker(1) to maximize the contact time of acid with the fracture face to get a high fracture conductivity in cool dolomite formations, which react slowly with acid. Maximum acid contact time is essential to create highly conductive etched channels on the fracture faces. After the designed fracture length is created, the injection is continued at certain rates to maintain the equilibrium with the fluid leak-off rate from the created fracture faces. This technique was proven to be effective in stimulating the relatively cool dolomite. Closed acid fracturing techniques(2) were designed to obtain high conductivity, especially for the formations with extra high fracture close stress.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".