The worldwide oil and natural gas industry is challenged by a number of fundamentals that few predict will change in the foreseeable future. They include:
• Demand for hydrocarbons is approaching production capacity;
• Many producing assets are depleting and water production is increasing;
• New fields are smaller, requiring economically viable development;
• New fields frequently have more complex geological structures;
• Drilling rig usage is close to 100%; and
• Minimizing environmental impact of drilling operations is mission critical.

These fundamentals are the driving force behind advancing many technological innovations and increased activity in certain drilling methods, including multilateral drilling.

Multilateral drilling
Multilateral drilling is the drilling of two or more horizontal production holes from a single surface location, normally with the objective to enhance productivity and lower overall cost.

Figure 1. A multilateral well drilled offshore Norway using INTEQ’s AutoTrak RCLS; CoPilot advanced drillstring dynamics diagnostics system and Hughes Christensen application-specific drill bits exposed 44,429 ft (13,542 m) of reservoir from a single slot. (Images courtesy of Baker Hughes INTEQ)
Drilling of multilateral wells is not as recent an innovation as many think. In the 1940s, John Eastman developed tools and techniques allowing drilling of horizontal and subsequently multilateral wells in California. In 1953, a Russian petroleum engineer, Alexander Grigoryan, drilled a multilateral well in the Bashkira field of Southern Russia. The results of his nine branch multilateral was that it produced 17 times the average production of offset wells but cost just 1.5 times the cost of a single branch well.

Since those pioneering days, technology has advanced at a rapid pace. Today’s market conditions and industry fundamentals are the new driving force behind an upsurge in multilateral drilling to address challenges faced by production companies.

Dependent upon individual circumstance, multilateral wells can help address the industry fundamentals summarized above. Advances in drilling technology, development of specialist techniques and growing experience have combined to test and push the envelope in multilateral drilling beyond what was previously considered feasible. The following examples illustrate how INTEQ’s answers-while-drilling approach is helping operators achieve key objectives of exploiting reserves to the maximum while simultaneously reducing the environmental impact and cost of field development.

Norway
Despite the fact than many believed the Troll field to be economically unviable, it is now
Figure 2. A typical MRC well drilled by in Saudi Arabia using INTEQ’s AutoTrak X-treme system coupled with CoPilot advanced drillstring dynamics diagnostic service and Hughes Christensen application specific drill bits to increase reservoir drainage area.
Norway’s largest producing oil field and is operated by Hydro. The reservoir covers an area of approximately 289.5 sq miles (750 sq km) but the pay-zone is relatively thin. To successfully recover the oil, innovative multilateral drilling techniques have been developed using advanced drilling technologies. The multilateral wells drilled here are some of, if not the most, complex in the world. Not only must the laterals be positioned within very tight target tolerance relative to the gas-oil-contact (GOC), but they are often geometrically complex, traversing through challenging formations and frequently of extended reach proportions. By positioning the legs precisely relative to the GOC, gas breakthrough is delayed and oil production rates are maintained for a longer period compared to single leg wells. Figure 1 shows an example of a five-branch multilateral well drilled on Troll. This single well exposed a total of 44,429 ft (13,542 m) of reservoir from one slot. As a result of extensive multilateral wells, to date, Hydro has drilled approximately 559 miles (900 km) of hole from spud to total depth on 130 wells in Troll. Incredibly, over 341.5 miles (550 km) of that total drilled distance is horizontally in the reservoir.

Saudi Arabia
To improve production and reservoir drainage area per well drilled, Saudi Aramco frequently drills maximum reservoir contact (MRC) wells in the Kingdom of Saudi Arabia. These multilateral wells are geosteered to and through the reservoir sweet spot.

Planned as three dimensional multilaterals with up to five legs, each leg is drilled in turn using retrievable whipstocks to initiate the exit. Through utilization of MRC multilateral wells, production is increased at a lower cost per well to help meet the increasing demand for oil. Figure 2 shows a typical Saudi Aramco MRC well draining a larger area of a reservoir than any single leg could achieve onshore Saudi Arabia.

India
The limestone reservoir of an oil field located offshore Mumbai, India, exhibits a coning dominated production profile. This is a significant issue on this field because not only does water or gas coning dramatically reduce oil production rates, but also the reservoir is driven by a natural gas cap, and any depletion of the gas cap could potentially reduce ultimate field recovery.

To address this, horizontal drilling was employed from an early stage in the field’s development. However, experience showed that coning remained a significant challenge as
Figure 3. A precisely positioned multilateral well, drilled using INTEQ’s AutoTrak X-treme system and Hughes Christensen application specific drill bits, to reduce pressure drawdown and eliminate coning of undesired fluids for increased production and improved ultimate field recovery.
the pressure drawdown along single leg laterals further encouraged coning, especially if the laterals were not drilled perfectly horizontal and water hold-ups occurred in the “dips.” This resulted in the need for a stop-cocking schedule to allow the cone to recede, resulting in production loss. To improve the situation, a major infill drilling campaign called for the use of more precisely positioned and flatter multilateral wells to reduce overall pressure drawdown and tendency for water hold-ups to occur. By achieving this, it was anticipated that gas and water coning would be significantly reduced, thereby increasing oil production per well and preserving the gas cap for improved overall field recovery.

Analysis of the performance of the more precisely positioned multilateral wells showed that they were all producing at the solution gas-oil-ratio (GOR), indicating that no gas was being coned from the gas cap — thereby preserving the reservoir drive mechanism and improving the overall field recovery factor. Figure 3 shows an example of a multilateral well drilled in this field.

Conclusion
Recent advances in drilling and evaluation technology, a growing experience base and recognition of what can be achieved are driving an increasing number of operators towards multilateral wells for their field developments. When applied correctly, the demonstrated benefits of multilateral wells include improved productivity, lower cost per boe produced, improved field recovery, delayed and reduced water cut and lower environmental impact. As a result, the traditional boundaries of what has previously been achieved are increasingly being tested — moving them to new levels and increasing multilateral drilling’s return on investment.

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