[Technical white paper] Advanced Big-Bore Refrac Systems: Optimizing Reservoir Re-Development & Wellbore Integrity
Next-Generation Big-Bore Re-fracturing Completion String
Welltech introduces a simple, highly stable, and cost-effective secondary completion design scheme. This system is widely utilized globally to revive production in mature, low-permeability, and low-abundance oil and gas reservoirs.
Engineered Mechanical Architecture
The complete completion string is deployed efficiently in a single run (one trip). The integral joint casing robustly carries the specialized liner hanger and packer assembly to mechanically isolate the compromised original casing. Crucially, the Welltech Re-fracturing string maintains an ultra-large internal diameter (Big-Bore ID). This configuration maximizes long-term hydrocarbon production channels and guarantees unrestricted clearance for subsequent downhole well intervention operations.
Core Technical Advantages & Operational Flexibility
- Versatile Deployment: Fully compatible with both previously cemented casings and uncemented open-hole completion strings.
- Sleeve-Integrated Efficiency: Can be seamlessly integrated with downhole sliding sleeves, enabling selective re-fracturing without the need for re-perforation or bridge plugs. This significantly minimizes local water consumption and prevents excessive pumping matrix costs.
- Plug-and-Perf Compatibility: Can operate seamlessly without sliding sleeves, fully supporting subsequent soluble bridge plugs and tailored re-perforation to safely initiate new stimulation intervals.
- Zonal Isolation & Remediation: Engineered to perfectly seal severe casing damage zones and original depleted perforation intervals. It can selectively shut off unwanted downhole fluid conduits, such as active water-producing zones.
- Wellbore Validation: Provides full pressure integrity across the rehabilitated wellbore to verify comprehensive long-term asset integrity.
Alternative refracturing methods:
|
Technology |
Principle |
Advantage |
Disadvantage |
|
Fluid blocking steering
|
A fluid or particle plug is used to perform selective fracturing |
1.Low cost
2.Easy to use
|
1.If a zone is not sealed, resulting in fluid loss or mud loss, it will damage the formation and even affect the adjacent well.
2.When unsealed, incomplete cleaning or plugging can result in damage to the formation, especially in dry gas Wells, and overcleaning can result in proppant impact.
3.Method to verify casing integrity and pressure performance of chemical plugging agent;
4.It's hard to tell if it worked.
|
|
Frac ball blocking steering |
The perforation is blocked by the ball with small aperture, and then the selective fracturing is carried out |
1.Low cost
2.Easy to use
|
1.If the fracturing is interrupted temporarily, the sealing of the ball will fail;
2.The uncertainty of sealing point is too great, resulting in insufficient accuracy of repeated transformation;
3.Because of the shape characteristics of the ball, it can not work on the sliding sleeve or the slotted pipe in the original well.
4.Non-soluble pellets cannot be recovered, leaving them in the well would be detrimental to subsequent operations.
5.The premise is that the casing is not damaged and there is no major damage;
|
|
Coiled tubing straddle refracturing |
The straddle-packer was run using coiled tubing for selective fracturing |
1.Adjustable sliding sleeve
2.recyclable
3.The bottom hole pressure can be monitored
|
1.High cost, low durability;
2.Long horizontal section cannot be used;
3.Small fracturing channels can not meet the fracturing design requirements of the displacement;
4.There is a risk of the tool falling into the well.
|
|
Liner recementing |
The original casing was re-cemented by running a small liner/casing |
1.Large inside diameter
2.Casing repair
|
1.Because the annular clearance between the casing and the original casing is too small, the cementing circulation is difficult.
2.Cementing cement can cause formation damage at the original perforating point.
3.The dog leg of the casing is too large, resulting in difficulty in running.
|
|
Expandable liner technology |
A small expansion liner was run into the original casing to restore well integrity |
1.Large inside diameter
2.Casing repair
|
1.In the expansion from the bottom to up expansion, there may be stuck;
2.The expansion ratio is not consistent at different perforating stages
|
Introduction to the Re-Frac String
Welltech introduces a simple, highly stable, and cost-effective secondary completion design scheme. This system is widely utilized globally to revive production and optimization in mature, low-permeability, and low-abundance oil and gas reservoirs.
The entire completion string is engineered for efficient deployment in a single run (one trip). The integral joint casing robustly carries the specialized liner hanger and packer assembly to mechanically isolate the compromised original casing. Crucially, the Welltech Re-fracturing string maintains an ultra-large internal diameter (Big-Bore ID). This configuration maximizes long-term hydrocarbon production channels and guarantees unrestricted clearance for subsequent downhole well intervention operations.
String Technical Advantages
- Versatile Deployment: Fully compatible with both previously cemented casings and uncemented open-hole completion strings.
- Sleeve-Integrated Efficiency: Can be seamlessly integrated with downhole sliding sleeves, enabling selective re-fracturing without the need for re-perforation or bridge plugs. This significantly minimizes local freshwater consumption and prevents excessive pumping matrix costs.
- Plug-and-Perf Compatibility: Can operate seamlessly without sliding sleeves, fully supporting subsequent soluble bridge plugs and tailored re-perforation to strategically initiate new stimulation intervals.
- Zonal Isolation & Remediation: Engineered to perfectly seal severe casing damage zones and original depleted perforation intervals. It can selectively shut off unwanted downhole fluid conduits, such as active water-producing zones.
- Wellbore Integrity Validation: Provides full pressure integrity across the rehabilitated wellbore to comprehensively verify long-term well integrity.
String parameters:
|
Specifications |
||||
|
Inside diameter of original casing/base pipe |
Maximum outside diameter of refract string |
Minimum inside diameter of refract string |
Pressure rating psi[MPa] |
Temperature rating ℉[℃] |
|
in[mm] |
in[mm] |
in[mm] |
||
|
4.892”[124.26] |
4.57” [116] |
3.386” [86]/3.661[93]” |
10,000 [70] 15,000 [105] |
300 [150] 400 [204] |
|
4.778”[121.36] |
4.488”[114] |
3.11”[79] |
||
|
4.67”[118.62] |
4.37”[111] |
2.992”[76] |
||
|
4.5”[114.3] |
4.213”[107] |
2.834”[72] |
||
|
4”[108.62] |
3.937” [100] |
2.441” [62] |
||
|
4”[101.6] |
3.661” [93] |
2.441” [62] |
||
Construction Steps (Re-fracturing with Slim-Hole Bridge Plugs):
- String Configuration: Assemble the downhole deployment sequence in order: guide shoe ➔ TOE sleeve or ball sleeve ➔ multiple HES isolation packers ➔ HYA-1 liner hanger ➔ production string.
- Wellbore Preparation: Run the watermelon milling tool combined with round head milling assembly to clean the wellbore (simulating the re-fracturing string length and Maximum OD).
- Casing Clean-Out & Drift: Deploy the lower-diameter drift gauge and specialized scraper assembly (simulating re-fracturing string length and OD) to circulate the well clean and ensure unrestricted clearance.
- Tripping In: Connect the completion string segments and trip into the wellbore to the target depth.
- Packer Setting: Drop the setting ball to hydraulically set the downhole packer assembly.
- Integrity Testing: Pressurize the production casing annulus to verify comprehensive zonal isolation and wellbore integrity.
- Initial Stage Initiation: Pressurize the wellbore to activate the TOE sliding sleeve or drop the targeting ball to open the sliding sleeve, initiating the first-stage re-fracturing operation.
- Sequential Stimulation: Proceed with the subsequent dissolvable bridge plug deployment combined with multi-stage perforation and fracturing operations (Internal diameter of the string is maintained at a maximized 86 mm).
- New Interval Isolation: If alternative or new perforating intervals are required, pre-deploy two HES isolation packers to straddle the newly targeted perforating zone in advance.
- Extended Multizone Recovery: Continuous and infinite differential multi-stage re-fracturing can be reliably achieved with robust cross-packer hydraulic support.
