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Development and Testing of Underbalanced Drilling Products
Project Number

To develop a new lightweight drilling fluid additive that will significantly reduce underbalanced and deep water drilling costs, and reduce formation damage during drilling and completion operations.


Maurer Engineering, Inc.
Chevron Research Technology Center
MUDTECH Laboratories, Inc.


Drilling underbalanced in under pressured and depleted reservoirs often requires a fluid with a density lower than that of water (specific gravity < 1.0). Current underbalanced operations in these reservoirs can be carried out using air, mist, or foam. However, many operators are reluctant to drill underbalanced with foam because of the difficult hydraulic calculations required and the general lack of information and training relative to underbalanced drilling. Thus, one of the project’s objectives was to develop a user-friendly PC-based foam-drilling model that can accurately predict pressure drops, cuttings lifting velocities, foam quality, and other foam-drilling variables. The model allows operators and service companies to easily and accurately predict pressures and required flow rates at the surface and under downhole conditions for foam drilling and work-over operations.

The addition of air or gas to the drilling fluid can also cause many problems, so a second objective of the project was to develop a lightweight, incompressible drilling fluid that will allow underbalanced drilling in low-pressure reservoirs without the limitations commonly associated with existing lightweight fluids. A new lightweight solid additive (LWSA) fluid was developed and tested both in the laboratory and in the field.

Accomplishments (most recent listed first)
Light Weight Solid Additives
Light Weight Solid Additives

The PC-based software, FOAM, was developed for planning and analyzing operational parameters during foam drilling projects.The model calculates pressure responses and flow behavior of foam fluids. Any one of three rheology models may be selected by the user, and the model can handle any combination of liquids and gases injected while drilling. Data are input in a series of four input windows and includes a general well description, directional survey data, drill string and wellbore configuration, and drilling parameters such as injection rates of liquid and gas, injection fluid properties, drilling rates, and drill-cuttings descriptions. After executing the program, an operation analysis or sensitivity analysis of the output data can be performed. The output from FOAM was validated by comparing it to other models, existing laboratory data, and actual field measurements.

While the computer model was under development, lightweight, incompressible fluids were constructed using commercially available hollow glass spheres. These fluids were tested in the laboratory and in the field. In the lab, sphere concentrations below 40% by volume lightweight muds behaved similarly to conventional drilling fluids. The effects of conventional solids control equipment on the glass spheres and on the whole mud were also measured with regard to sphere damage and recovery. The conventional equipment did not damage the spheres. Hydrocyclones proved to be the most effective equipment in maintaining the mud. In August 1996, the LWSA fluid was successfully used in two wells drilled in the Midway-Sunset Field near Bakersfield, California for Mobil Oil Company. The spheres were in the drilling mud at concentrations of up to 20% by volume while over 3,000 feet of hole were drilled.

Current Status

and Remaining Tasks: 
This project has been completed and the PC-based “FOAM” model has been made available for use by the oil and gas industry. Industry's recognition of the potential of the LWSA technology was acknowledged by the Society of Petroleum Engineers published technical report in the November 1997 issue of the Journal of Petroleum Technology (JPT). This acknowledgment is expected to lead to added commercialization interest.

Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

Maurer Engineering, Inc. – Bill McDonald (713-683-8227 or
NETL – Roy Long (918-699-2017 or