Hydraulic fracturing using high-boiling fraction of oil as a fracturing fluid
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-07-18 |
| Journal | Kazakhstan journal for oil & gas industry |
| Authors | Moldir A. Mashrapova, Nurbol Tileuberdi, Dairabay Zhumadiluly Abdeli, S. M. Ozdoyev, Ardak S. Iskak |
| Institutions | Satbayev University, Institute of Geological Sciences |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the use of high-boiling oil fractions (components with carbon atoms > C8) as a novel, cost-effective fracturing fluid for hydraulic fracturing (HF) in complex, low-permeability oil reservoirs in Kazakhstan.
- Core Problem Addressed: Traditional water-based gel fracturing fluids are ineffective in heterogeneous, multi-layer reservoirs due to clay swelling and adsorption of long-chain gel molecules, leading to severe formation damage and high water cut (WC).
- Novel Solution: Utilizing a high-boiling fraction of degassed crude oil, obtained via a simple single-stage distillation process, as the primary fracturing fluid.
- Performance Improvement: Experimental results demonstrated a significant increase in core permeability, ranging from 4x to 5x after treatment with the high-boiling oil fraction.
- Economic Advantage: The oil-based HF method resulted in an estimated 35% reduction in operational costs compared to water-based treatments, primarily due to reduced water handling and stimulation volume.
- Water Cut Control: The oil-based fluid is stable at high reservoir temperatures and avoids the risk of fracture extension into adjacent water-saturated layers, which typically causes high WC (up to 80% observed after water-based HF).
- Field Potential: Application of this method in the Arystan field productive horizons showed a substantial increase in average monthly oil production (approximately 400 tons).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target Oil Fraction | Components with C atoms â„ C8 | N/A | Used as the fracturing fluid base. |
| Fluid Preparation Temperature | 200-220 | °C | Separation temperature for high-boiling fraction. |
| Reservoir Oil Viscosity (Arystan) | 4-12 | mPa*s | Viscosity of native oil in the productive horizon. |
| Fracturing Fluid Viscosity | 57 | mPa*s | Viscosity of the heavy oil fraction at reservoir temperature. |
| Initial Water Cut (Pre-HF) | 20 | % | Typical water cut before stimulation. |
| Water Cut (Post Water-Based HF) | 80 | % | Observed water cut increase due to fracture extension into water layers. |
| Oil Production Increase | ~400 | tons/month | Average increase after oil-based HF application. |
| Operational Cost Savings | ~35 | % | Cost reduction compared to water-based gel HF. |
| Core 1 Permeability Increase | 1.71 to 8.59 | ”m2 | Permeability coefficient increase (5x). |
| Core 4 Permeability Increase | 0.44 to 1.77 | ”m2 | Permeability coefficient increase (4x). |
Key Methodologies
Section titled âKey MethodologiesâThe study involved two main phases: preparation of the high-boiling fracturing fluid and laboratory simulation of the hydraulic fracturing process using reservoir core samples.
1. Fracturing Fluid Preparation (Single-Stage Distillation)
Section titled â1. Fracturing Fluid Preparation (Single-Stage Distillation)â- Feedstock: Degassed crude oil from the target field is used as the raw material.
- Heating: The crude oil is fed into a tubular furnace and heated to a temperature range of 200-220°C.
- Separation: The heated oil is directed into a two-section separation unit containing horizontal plates (trays).
- Fraction Collection:
- Lighter fractions (boiling point less than 200°C, C atoms less than C8) are collected from the upper plate.
- The heavy, high-boiling fraction (boiling point greater than 200°C, C atoms greater than or equal to C8) is collected from the lower plate.
- Cooling and Storage: Both fractions are condensed and stored in separate reservoirs for use.
2. Laboratory Hydraulic Fracturing Simulation
Section titled â2. Laboratory Hydraulic Fracturing Simulationâ- Core Preparation: Reservoir core samples are obtained via diamond drilling, cleaned of dust and debris using high-pressure air, and weighed.
- Initial Saturation (Light Oil): The core is placed in the testing apparatus. Light oil (simulating native reservoir fluid) is pumped through the core at high pressure, and the initial permeability coefficient (Kpr) is measured.
- Fracturing Fluid Injection (Heavy Oil): The high-boiling oil fraction (fracturing fluid) is injected into the core at high pressure (Pkenzh > Ptau, where Ptau is the local rock pressure) to simulate fracture initiation and extension.
- Acid Treatment (Optional/Sequential): An acid mixture is injected following the heavy oil fraction to enhance the fracture conductivity.
- Displacement (Pushing Fluid): A pushing fluid (degassed crude oil) is injected to displace the fracturing fluid and acid mixture from the fracture zone.
- Final Measurement: Light oil is pumped back through the core, and the final permeability coefficient is measured to quantify the improvement achieved by the treatment.
Commercial Applications
Section titled âCommercial ApplicationsâThis technology is highly relevant for Enhanced Oil Recovery (EOR) operations, particularly in mature fields characterized by complex geology.
- Low-Permeability Reservoirs: Applicable for stimulating tight oil formations and low-permeability sandstones or carbonates where conventional water-based fracturing is ineffective.
- Heterogeneous/Multi-Layer Fields: Ideal for fields with strong compartmentalization and alternating permeable and impermeable layers, such as those common in Kazakhstan, where precise fracture control is necessary to avoid water zones.
- Water Control Management: Used as a primary stimulation method in reservoirs with high water saturation or proximity to water-bearing layers, significantly mitigating the risk of premature water breakthrough and high water cut.
- Cost-Effective Stimulation: Provides a lower-cost alternative to complex, chemically-intensive water-based gel systems, reducing the need for expensive gel additives, water purification, and specialized clay stabilization chemicals (e.g., KCl).
- High-Temperature Environments: Suitable for deep, high-temperature reservoirs where water-based gels tend to degrade and lose viscosity, as the high-boiling oil fraction maintains stability.
View Original Abstract
Background: In recent years, there has been a trend towards deterioration in the structure of residual reserves at the fields of Kazakhstan. A significant part of the reserves is located in low-permeability reservoirs and in the zones not covered by flooding. The main factor negatively affecting the productivity and efficiency of development is the heterogeneity of oil reservoirs. Oil-saturated formations are an alternation of permeable oil-saturated sand or limestone and impermeable clay or dolomite layers, lenses and interlayers. Up to 1020 interlayers can be distinguished within the reservoir, which indicates a strong compartmentalization of the reservoirs. Due to the complexity of the structure of oil deposits, it is very difficult or impossible to ensure complete drainage of the entire volume of the deposit and complete coverage of oil displacement by water into production wells through injection wells. Aim: Increasing oil recovery in a cost-effective way. Materials and methods: Experimental studies of the processes of impact on the bottomhole formation zone with high-boiling oil components were carried out using a laboratory machine for diamond drilling, an installation for determining the permeability of a rock in terms of liquid and gas, an installation for determining oil viscosity, and an installation for pumping fracturing fluid into the reservoir model. Results: As a result of applying the hydraulic fracturing method using high-boiling oil components, it is possible to increase the permeability of low-permeability formations and significantly increase oil recovery. Conclusion: Due to the geological structure of multi-layer oilfields, water-based gel fracturing fluids to increase oil flow to wells are considered ineffective due to the adsorption of gels with long molecules in the pores of the formation and swelling of the clay particles of the reservoir when they interact with the water-based fluid.