Press Release 8th May 2001

SPE – 68911: Stimulation of a Producing Horizontal Well Using Enzymes that Generate Acid In-Situ - Case History

For Immediate Release:

Cleansorb is pleased to announce that SPE paper 68911 concerning the successful application of in-situ acidizing to stimulate production from a horizontal well is being presented as a poster and manuscript in conjunction with Chevron Oil Congo Ltd. at the SPE European Formation Damage Conference 21-22 May 2001, The Hague, The Netherlands. The paper describes how treatment fluid was mixed at surface and bullheaded into the horizontal section to allow downhole acidizing to occur during shut in. This resulted in clean up of residual oil based mud damage remaining from when the well was originally acidized with 15% HCl by jet washing with a work string immediately after the completion. Production results following the recent in-situ acidizing treatment have been excellent. Well tests as high as 759 BOPD have been recorded after the treatment compared to less than 100 BOPD before the treatment.

The downhole acidizing process, Arcasolve^TM, is a unique technology for in-situ acidizing of wellbores and the adjacent formation to remove acid soluble drilling damage and formation damage. It is especially suited to situations where placement of conventional reactive acids is problematic e.g. acidizing long horizontal wellbores. Cleansorb can also incorporate selected polymer breaking enzymes into Arcasolve^TM formulations to provide single step combined acidizing and polymer breaker treatments. This is particularly effective for clean up of water based drilling mud damage in horizontal wells.

Recent Arcasolve^TMtreatments to clean up residual water based mud damage and oil based mud damage in horizontal wells have been particularly successful (further details available from Cleansorb on request).

Further information is available from:

Dr. Ian McKay or Dr Ralph Harris

Cleansorb Ltd, Surrey Technology Centre , 40 Occam Road, Surrey Research Park, Guildford, Surrey GU2 7YG, U.K.

Tel. ++44 (0)1483 295090

Fax. ++44 (0)1483 845358

email:

Notes for editors:

1. Arcasolve^TM has been developed by Cleansorb Limited, based at the Surrey Research Park in Guildford, Surrey, UK. The process combines enzymes (biological catalysts) with suitable chemicals to generate organic acid at a controlled rate in the fluid injected into the wellbore or formation. The bulk of the acid is produced after placement of the fluid, permitting the efficient and even delivery of acid to the target zones maximizing the production rate of the well and its value to the operator. Arcasolve^TM is environmentally friendly and very low hazard. Conventional acids are hazardous in use and generally require the use of toxic corrosion inhibitors.

2. A catalyst is a compound which promotes a chemical reaction without itself being consumed. The catalyst used in the Arcasolve^TM process is an enzyme. Enzymes are chemical compounds found in nature. They are however single chemical compounds which can be manufactured to the usual standards of purity of industrial chemicals.

3. Although Arcasolve ^TMis a biotechnological process it should be clearly distinguished from previous stimulation processes based on bacteria. Using enzymes confers many advantages including a high level of process control, high yield and better thermotolerance. Enzyme based systems are also particulate free.

4. Arcasolve^TM has been granted Millennium Products status by the UK Design Council. This means that it has been independently recognized as an innovative product which will change working practices in the 21st century.

5. Cleansorb Limited, based at the Surrey Research Park, Guildford, Surrey, UK, is a privately owned biotechnology company which specializes in developing enzyme-based processes which assist oil and gas production. Contact: Ian McKay or Ralph Harris, Tel. ++44 (0) 1483 295090 Fax. ++44 (0) 1483 845358.

6. In addition to Arcasolve^TM, Cleansorb has other award winning enzyme-based processes under development which allow the controlled deposition of gels, minerals or resins in underground reservoirs. These have a number of applications in oil and gas production.