A majority of industry operators and service companies have adopted directional drilling collision avoidance rules based on stringent controls to prevent surface collisions and consequent human and environmental damage. These rules are found to be severely restrictive for the optimal positioning of wells through deeper reservoir zones where the level of damage from collision can be contained.
A new method is proposed that retains existing rules for avoidance of shallow (severe outcome) collisions and provides the option for use of risk based rules in deeper sections of wells where the outcome of a collision would not be as severe. The risk level of collision with respect to any offset well is calculated and then converted to a Risked Clearance Factor, an established standard for evaluating different levels of collision tolerance in wells.
Deep intersections have several characteristics which require separate treatment from shallow intersections. They have high convergence angles which minimize the physical space and distance where a collision may occur and they have lower economic risks of a collision relative to the cost of corrective action.
This method has been implemented in a field area of rapid prospect planning and development. The rules are designed to be simple and practical in order to reduce planning and drilling cycle time. A matrix of risk elements, specific to the field area is presented for different depths of collision to help to derive the level of tolerable risk. A case history is presented that shows the clear benefit of utilizing the alternate method.
Chevron's Thailand Business Unit (COTL) had previously identified multiple instances where Asset teams desired to position a development well close to an abandoned exploration well in order access the maximum volume of potential reserves. In many of these instances, the well planning team in the Drilling group was unable to deliver a well in the desired target location(s) due to constraints imposed by the existing Collision Avoidance policy. In some instances a significant decrease in Net Present Value was realized due to the less than optimal reservoir position. Both the Asset and Drilling teams identified the need to develop alternate methods for placing a well in the most desired location in order to access the most reserves while still maintaining a safe working condition.
In addition to the above, it was also identified that the existing Collision Avoidance policy included provisions for closing in and depressurizing producing wells adjacent to active drilling wells. While this practice (to varying degrees) is standard throughout Chevron and the industry in general, it was felt that a review of COTL's current practices was required in order to insure that the policy was not over conservative. The upside of this analysis would be less shut-in days for adjacent wells translating to fewer days of deferred production.
With these drivers in mind, a project team consisting of COTL and Chevron Corporation Energy Technology (ETC) personnel was formed to investigate an alternative collision avoidance methodology specific to the unique nature of the COTL drilling environment.
