Horizontal Drilling FAQs

Why should I consider horizontal drilling for my reservoirs?

Horizontal wells have the potential to dramatically enhance the economics of your project. Horizontal wells are placed in a reservoir precisely to maximize hydrocarbon (oil and gas) production. Horizontal wells provide added wellbore exposure to the reservoir in a geometry that allows an operator to do the following:

• Maximize hydrocarbon recovery rates and project economics
• Spread out the pressure drop across a longer interval of wellbore minimizing water coning
• Repenetrate a reservoir to get away from historical water coning and recover reserves that would otherwise be stranded
• Take advantage of horizontal well geometry for secondary recovery projects

How do I determine which of my reservoirs are valid horizontal drilling candidates?

Collect sufficient reservoir and production data to be able to build a computer model of the reservoir. Perform history matching to gain confidence on the simulation results. Predict the production effects of various horizontal completions options to determine the most reasonable approach to applying horizontal wells to accelerate reserve recovery.

How do I choose which horizontal drilling system is appropriate for my reservoir?

An engineering assessment of the completion techniques necessary to economically recover the reserves will largely determine if the horizontal well can be an openhole completion or will require tubulars placed in the curve and/or in the horizontal sections. The critical issue is wellbore stability and the need for zonal isolation to construct a low maintenance, long life completion.

What are the costs associated with directional drilling using various drilling systems?

Based on studies of over 25,000 horizontal wells world wide, an expert has recognized key relationships between horizontal and vertical well costs.

• One third of horizontal wells are not economic successes
• When the cost ratio for a proposed horizontal well approaches or exceeds 2.5 to 3.0 times the cost of a vertical well in the same field, the chances for an economic success are greatly reduced

This means when evaluating the cost benefit of the horizontal drilling candidate, if the proposed drilling and completion design costs are approaching 2.5 to 3.0 times the cost of a typically completed vertical well in the field, there is very little room for error and proceeding with assumptions rather than data can become very costly.

Do you need to drill a new well or can you use an existing one?

A new well is not always necessary. Many techniques are available to use existing vertical wells and exit through the casing. Depending on the completion techniques required, the costs for using existing wells compared to new wells, will generally favor existing well utilization. However, geologic considerations and current reservoir data collection opportunities must be weighed carefully with any potential cost savings.

Will an open hole provide a satisfactory completion technique?

This is determined by understanding the long-term borehole stability issue associated with the candidate reservoir. This issue is critical in determining the answer to open hole completions versus installing casing or liners in the curve or lateral sections.

How can your drilling and completion operation minimize formation damage?

Overbalanced, poorly designed and maintained drilling fluids will cause excessive formation damage. The lower the bottom hole pressure (BHP) of the target reservoir, the more difficult it is to mediate any damage caused from the drilling and completion process.

Underbalanced drilling, when properly conducted, will help to minimize formation damage reducing or eliminating remedial action required to restore well bore productivity. The drilling fluids needed for underbalanced operation is determined by reservoir BHP. For low BHP situations, air or air mist/ foam drilling may be required.

If you choose to drill underbalanced, can you safely drill with air?

Air drilling oil and gas wells has been an accepted industry practice for over 60 years. Grand Directions has been drilling with an air/foam-mist system for the last three years with no safety problems.

What kind of rig is necessary for horizontal drilling?

When new wells are planned to be drilled horizontal, the drilling rig is usually employed to drill both the vertical and horizontal portions of the wells. However, depending on the equipment requirements for the curve and lateral sections, a smaller (less costly) workover rig may be moved in after the drilling rig has completed the vertical section.

When existing wells are to be used for horizontal completions, often a workover rig can be outfitted to handle the physical requirements of the operations less expensively than employing a drilling rig to do the work.

How do you determine and control the actual direction and location of the wellbore?

This is a two-pronged question:

• How to determine the best direction to drill is determined by a thorough study of the geologic deposition and structural history and the reservoir fluid flow patterns resulting from withdrawal and injection activities. The size of the target and any spatial constraints associated with the target must be determined and specified in the well path plan.
• How to control well path direction is the realm of the drilling operations. Many improvements in the directional surveying and tool steering services have occurred in the past 15 years. Generally, the tighter the need for wellbore placement control, the more expensive the process.

Can you run open- and cased-hole logs in horizontal wells?

The idea of directional drilling into a known reservoir should produce open hole logs of boringly consistent petrophysical measurements. This has not been the experience most people have had with regards to openhole logs from horizontal wells. When fracture identification and orientation with respect to the well bore are critical to the productivity of the horizontal well, openhole logs become keystone to the horizontal well project.

For example, understanding the injection profile of a horizontal injection well, proved invaluable in reconfiguring our Wolco horizontal well project.

If necessary, how do you stimulate horizontal wells?

Many horizontal wells drilled today in the various "oil shale" plays in the USA require massive hydraulic fracture stimulation treatments, often costing as much as the horizontal section of the well. The wells must be drilled and completed with this in mind as this is the technique that has evolved in a particular basin, providing the most economical cost benefit ratios.