CB Petro's Mexican Reservoir Characterization Experience
The Team at CB Petro while working with Pemex in Mexico, had the great opportunity to characterize most of the major oil fields in the Mexico offshore and a few key onshore fields. In most of the fields studied, the Cretaceous Reservoir has been the primary target but we also characterized the Jurassic, Eocene and Oxfordian reservoirs. However, it was the understanding and characterization of the Cretaceous Reservoirs that was the biggest challenge. The Cretaceous is a very complex reservoir that lies outside most traditional oil or Service Company’s area of expertise. There is no single discipline or tool that can be used to characterize the Cretaceous. It was a fully integrated approach from Geoscience, Petrophysics, 3D modeling, Engineering and Simulation that led to the final understanding of this reservoir.
Cretaceous Secondary Porosity Reservoir
The Cretaceous reservoirs in most offshore fields have very low matrix porosity. Secondary porosity dominates the reservoir and is primarily responsible for storage and delivery. The example below shows analogs to what might be expected in the Cretaceous reservoir. Each field/reservoir we studied were slightly different, but generally we saw low matrix porosity, fractured, vuggy carbonate reservoirs with large solution features in some fields. The biggest difference between the offshore fields was the depositional facies, the structural timing, the amount of secondary porosity development and the timing of hydrocarbon migration. The borehole image shown in the bottom left below is from a Pemex paper. This paper provided a key to the quantification of secondary porosity using the borehole image log. We have developed and employed similar techniques on each Cretaceous reservoir in order to compute a mega+ porosity value from borehole images. Traditional open-hole logs such as sonic and density often underestimate porosity in extremely heterogeneous (vuggy) carbonate reservoirs dominated by secondary porosity. However, full waveform sonic data was found to be quite useful. Contrary to most reservoir studies, porosity could be one of the largest uncertainties in this type of reservoir.
Our experience onshore was a bit different. The onshore Cretaceous reservoirs that we studied were primarily fractured with very little in the way of solution feature development other than pin-point vugs. Also, contrary to our offshore Cretaceous reservoir experience, the core recoveries onshore in the Cretaceous were quite good. Our core descriptions for the onshore Cretaceous suggest a dense carbonate with little to no oil stain except along the fracture surfaces. Here, fractures were everything. This description fits well in our paragenetic model integrating the depositional facies, structural formation, development of solution features, cementation and timing of hydrocarbon migration.
Experience
The team at CB Petro has conducted numerous in-depth Geoscience and Engineering studies on most of the major offshore oil fields from the Bay of Campeche and a few large onshore oil fields too. Working on integrated teams was the optimal way to approach these reservoirs. It is not only important to understand the reservoir from the Geoscience perspective, but also from dynamic point of view too. This is why most of us on the Geoscience side were intimately involved with the Simulation and production too.
Do you know that a pressure pulse from one side of some of these Cretaceous reservoirs could be felt nearly instantaneously across the field?
Are you aware that most of the Cretaceous reservoirs use Nitrogen injection from the crest for pressure maintenance and displacement? It was critical to track the current fluid contacts to better understand the existing rim of available oil and where to well placement.
What can be gleaned from the poor core recovery in the Cretaceous offshore or good recoveries onshore?
What tools were found to be best in characterizing the reservoir statically and dynamically?
Team Integration
Our combined experience and skills in characterizing the reservoirs of Mexico at CB Petro will jump-start your company's understanding of these reservoirs and move you further along the learning curve than by doing this on your own. This is our business. It is our opinion that this needs to be an integrated approach for no one discipline holds all the answers. We firmly believe that working in integrated teams provided the best solutions.
We are there for you
CP Petro is a group of experienced individuals that basically want to be of service to those that are moving into this challenging area of characterizing Mexican reservoirs. Please contact us at your earliest convenience.
