Probabilistic Methodology for the Classification and Selection of Intervals To Be Completed During the Exploratory Stage in Unconventional Reservoirs

Gallardo, Carlos Enrique (Ecopetrol) | Restrepo, Dora (Ecopetrol) | Castillo, Ruben (Ecopetrol) | Ardila, Sergio (Consultec)


SUMMARY: During the initial evaluation phase of an exploration project in unconventional reservoirs the intervals that will be completed should be prioritized, as a consequence, it is necessary to create a methodology to optimize the selection of intervals for stimulating. This selection is made more difficult at the beginning of the exploratory phase, especially in very thick formations (greater than 500 ft), where there may be several prospective intervals from the point of view of rock quality. Initial tests in vertical wells have a higher investment risk associated with the completion of unfavorable horizons for fracturing, i.e. failures during execution the hydraulic fracturing or great difficulty for proppant admission, therefore an inefficient fracture is created for migration of reservoir fluids into the well. As a result of interdisciplinary work, a methodology for selecting horizons with greater probability of success in hydraulic fracturing (under the Colombian tectonic environment) and for incorporating resources in a vertical well in an unconventional reservoir that has several prospective horizons was generated. Additionally, for the horizons with potential production of gas and gas condensate, a prioritization criterion was established, taking into account the effect of pore pressure decline on the matrix permeability (stress sensitivity).

The proposed methodology is based on: a) generate and interpret an anisotropic geomechanical model, b) selecting intervals that meet the quality criterion for completion in terms of elastic properties, c) generate a probabilistic solution for the distribution of the minimal horizontal stress, fracture gradient and net pressure, d) classifying selected intervals based on the likelihood of having a favorable complexity fracture, e) classifying the intervals in terms of mobility of fluids in the reservoir, f) sorting the prospective intervals in terms of value generation associated with each resource. By applying the methodology it is achieved for example discard prospective horizons with good rock quality, high probability of success of completion but low incorporation of resources, another possibility is to discard horizons with good rock quality, good fluid quality but low probability of successful completion. As a result of the exercise the operator managed to prioritize investment in 3 of the 6 prospective horizons for completion and testing.