Mature assets by definition are oil and gas fields that have been producing for upwards of twenty-five years. Thus, the Niger Delta Basin is considered a mature oil and gas producing region, one with an abundance of highly prolific hydrocarbon dicoveries which includes several undeveloped prospects.
Mature assets present a distinct mix of challenges and opportunities, especially at a time when a wave of ambitious indigenous operators—grappling with widespread production decline—are projected to contribute around 60% of the country’s output.
Maturity in the Niger Delta signifies decades of sustained exploration and production activity. With the region currently accounting for up to 90% of Nigeria’s oil output and no new major fields expected to come onstream before the decade ends, the urgency to maximize value from these mature assets could not be overstated. Application of technology underpins the ability to breathe new life into mature fields and accelerate production of low cost barrels from existing wells with proximity to existing infrastructure.
Nigeria urgently needs to restore its production baseline of 2 million barrels of oil per day to help ease persistent macroeconomic pressures and for its energy security. In the short to medium term, realizing this target will largely depend on how efficiently independent operators, in joint venture with NNPC, can drill in-fill wells, reactivate dormant ones and optimize production from underperforming assets.
Driving Production Growth Through Innovative Technology
A proliferation of inactive wells dot the Niger Delta landscape—greater than 2000 in total with about 600 in the control of Seplat and Renaisance—representing greater than 150K locked in oil barrels. This presents a pool of assets that can only be unlocked through innovative, cost-effective and technology driven development strategies.
In what is best considered a technological paradigm shift and one of the major hallmarks of innovation in the oil and gas industry, Horizontal drilling, which fundamentally increases wellbore exposure across the lateral extent of the reservoir began to gain wide adoption around the mid-nineties and stand out till this day for its hydrocarbon recovery and production enhancement potential. Horizontal drilling is now applied more and more to reactivate and rejuvenate fields that are near or have reached their economic limit.
The upside potential for horizontal drilling is massive if applied properly and in the right field. Exposing more reservoir rock to the wellbore minimizes pressure drawdown.
Reduced pressure drawdown especially in low permeability reservoir of < 1 Darcy, in thin-thickness high permeability zones, or in vertical fractures, horizontal wells stabilize reservoir dynamics, minimizing risks like water coning or gas cusping that frequently compromise vertical wells (Joshi 1991). The result is enhanced recovery rates and better reservoir stability.
Horizontal drilling minimizes the need for multiple wells by draining larger reservoir areas with a single well. This reduces capital expenditure and operational costs while enhancing the field’s overall economics—a primary driver for upstream business operations.
Figure 1: Production Comparison—Horizontal Well vs. Vertical Wells in High GOR Oilfield In high gas-oil ratio (GOR) oilfields, horizontal wells significantly outperform vertical wells, producing higher volumes of oil (left) and smaller amounts of gas (right). This data from Canada’s Devonian Rainbow Reef Reservoir demonstrates how re-entry horizontal sidetracking enabled operators to extract oil efficiently without an excessive gas cut. (Source: McIntyre et.al. 1994).
Zeroing in on the Right Technology
Horizontal wells are typically grouped in four categories: Long radius, Medium radius, Short radius and the Ultra short radius – according to radius of curvature transversed by the well bore as it passes from the vertical to the horizontal.
The Ultra Short Radius (USR) re-entry and completion system is a rapidly deployable and cost-effective technology that expands the use of horizontal drilling in existing wells. Purpose-built to access bypassed reserves, enhance production from marginal wells, revive shut-in wells, and reduce water cut, USR technology unlocks asset value in ways conventional horizontal methods cannot.
Ultra short radius (USR) equipment can be used to re-enter a vertical well and drill a horizontal drain-hole with shortest possible radius of curvature (8-17m)* where the TVD consumed by curve is less than 17m and restricted to the pay zone by keeping high build up rate (close to 250° per 30m) and lateral departure of about 150m in length.
USR horizontal drilling is the preferred option in heterogeneous, low permeability, thin layered, semi-depleted, naturally fractured reservoirs or when coning of water / gas is expected to interfere with full recovery. Using USR horizontal drain holes, oil can be produced at low draw-down pressures keeping away water coning as long as possible and without reducing production rates.
Figure 2: Comparative Analysis of USR Sidetracking vs. Large Radius New Well
This diagram comparesUSR sidetracking (blue) andLarge Radius (LR) new well (red) in a middle east country, illustrating their distinct reservoir access strategies.
USR trajectory stays entirely within the Shugaba Reservoir, efficiently draining oil within an 800-foot radius while avoidingNazir Umur shale by sidetracking at the reservoir’s top. This eliminates the need foradditional casing strings, unlike LR wells, which encounter shale along their extended curve section.
The comparison highlightsUSR’s cost-efficiency, showing how shorter curve intervalsreduce drilling complexity, optimize reservoir exposure, and minimize casing requirements—key factors in improving well economics. While LR wells provide extended lateral reach, USR sidetracks unlock bypassed reserves near existing wellbores, offering a complementary development strategy.
Results from seven USR sidetracks in the documented case showIP increases of 1.9–5.5x over the original vertical wells, including one well improving from0 to 227 BOPD and another with a0.3x increase.
With a variety of applications in low producing wells, tightly spaced fields, wells with water coning, channel sands with surrounding shale and exploitation of attic oil, drilling low-cost horizontal wells from existing vertical, or deviated wellbores, using USR drilling technologies, will significantly improve oil recovery and economics of currently producing oilfields in Nigeriaand grow reserves.
In addition to significant cost savings achievable (Comparable with the cost of a conventional intervention and 40 – 50% below the cost of a new well), the application of the unique USRD intervention technology brings forward the window of opportunity to unlock up to 200K BOPD in eighteen (18) months – corresponding to increased well productivity factor range of 1.8 – 2.5.
Figure 3: Nigeria’s Production Ramp-Up Forecast (Notional)
USR Offers the Following Advantages Over Conventional Horizontal Drilling Systems:
- USR drilling enables kick-off point to be at a depth very near, or in numerous cases, inside the objective hydrocarbon zone itself. This is due to its ultra short ROC of 7-17m as compared to over 300m in the above chart.
- Downhole Pumps or Gas Lift Valves, for instance, can be placed at or near the top of the pay zone to maximize production efficiency and extend the productive life of the well due to lower abandonment pressures.
- USR drilling enables the landing of the well bore at a distance very near to original well bore in case of re-entry drilling from existing well i.e. Sidetrack, at 8-9m from original well bore as compared to a much greater distance of over 300m.
- Due to such low ROC, landing in thin targets near the existing well bore can be more easily achieved.
- It can eliminate the need for expensive electric wireline logging due to its ultra short vertical section and landing point from the original well bore from which geology, production and reservoir data are readily available.
- Tighter curves allow horizontal sections to be initiated nearer the existing well bore with known data. Often the objective pay zone is missed due to the presence of lenses or minor faults which are not identified by seismic or other field data.
- A more precise placement of the horizontal well bore allows for a more efficient development of closely spaced fields.
- Enables precision placement of a horizontal section across the objective hydrocarbon zone, at a very close distance to the kick-off point.
- The drilled distance from kickoff depth to end of curve depth is much shorter than conventionally drilled wells. USR curves require less than 20m of drilled hole as opposed to more than 500m.
- Shorter curves based on local benchmarks saves millions of dollars in drilling costs.
- In most cases where reservoir thickness permits, kickoff points can be set below problem zones with water, gas caps or shales that can be difficult to drill due to hole stability. The entire curve and lateral can be drilled in the producing formation and below cap rock.
- Wellbores are slim hole which allows for less expensive Workover Type Rigs or Hydraulic Workover Hoists, smaller pumps and circulating systems to be used.
- Multiple laterals can be drilled in opposing directions or in the same direction, landing at the same true vertical depth (“TVD”) or at varying TVD’s. Multiple Laterals can be Drilled From a Single Well-bore;
In conclusion, USR Drilling offers Nigerian operators a viable and cost-effective alternative technology that is especially well suited for use as a reentry tool in the “Brownfields” of the Niger Delta. Adopting the USR Drilling technology widely in Nigerian upstream operations could measurably improve key operational metrics – Unit Operating costs and Unit Development Costs – in line with recent government’s cost restructuring aspirations.
References
- Chi Zhang, Wei Zhou, Ningbo Cheng. 2016. “Overview of Rotary Steerable System and Its Control Methods.” IEEE International Conference on Mechatronics and Automation. Harbin, China: IEEE. 1559-1565.
- Hill, D, E Neme, and C Ehlig-Economides. 1996. “Reentry Drilling Gives New Life to Aging Fields.” Oilfield Review 4-17
- Hou, Cougar. 2010. Incremental Oil Recovery Technologies For Mature Fields. Jereh Group Internal Presentation.
- Ingold, Charles. 2007. “Short-Radius Drilling: A Decade of Development.” Drilling Contractor 74-76
Joshi, Sada D. 1991. Horizontal Well Technology. Tulsa, Oklahoma: PennWell Publishing Company.
- Kesonpat, K, and E Berkheimer. 2005. “Rima-8 H5 USR Re-Entry Sidetrack: Failure Analysis of ACPT Composite Drill Pipe Using Drilling Stress Simulations and Recommended Wayforward.” PDO Project Report, Well Engineering, Petroleum Development Oman, Muscat.
