Pacific Section AAPG Convention

Datapages, Inc.Print this page

Challenges And Values Of Formation Testing In Tight Sand In Monterey Formation Using Modular Dynamic Tester (MDT)


A vertical appraisal well was drilled in the southern San Joaquin Valley to evaluate two intervals in the Monterey Formation. The target reservoirs have decent porosity but low matrix permeability. The well will have comingled production, if completed in both zones. The purpose of the appraisal well is to properly characterize the reservoirs and evaluate technologies that can lead to the development of tight reservoirs in the area. A secondary objective is to understand the individual zone production such that we may target a single zone for future development. The completion and producibility of these tight intervals is still in debate and quite challenging. These zones will likely need to be frac stimulated due to very low permeability. This paper describes the challenges and values of formation testing using the Modular Dynamic Tester (MDT) run in the well. The MDT was selected to run to measure formation pressure, collect fluid samples for PVT analysis and test the frac closure pressure. A decision was made beforehand to run the MDT tool through drill pipe to avoid any potential drilling issues. However, this had less flexibility in moving up / down the hole and was time consuming. The tightness of the reservoir posed additional challenges to be able to collect fluid samples in a limited time frame and with conventional sample collection techniques. However, continuous onsite monitoring, on the fly changes in the sample depths in response to formation behavior, and optimization of sample chamber opening time enabled us to successfully collect one water and two oil samples. At two depths we were able to get reservoir pressure data that was more accurate than data from XPT. The sample is being currently analyzed for fluid properties which will help narrow down the uncertainties and aid in planning the stimulation of the well. This is especially important to prove and maintain the commerciality of the reservoir. Lessons Learned: 1. MDT is a proven technique but needs special attention including on-site monitoring when evaluating tight rocks. 2. Remote monitoring may not always be real time. Decision may need to be made on the fly. Best Practices: 1. Early engagement with Subject Matter Experts (SMEs) and vendor for job planning. 2. Ensure people in early engagement meetings are available during job execution. Challenges: 1. Running tool on drill pipe, though safer, is time consuming. 2. Persons executing the job were not involved in pre-job planning.