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New Method of Defining Net Thickness in the Bone Spring Sandstones to Identify Prospective Reservoirs Using Petrophysical Attributes and Stochastic Simulation Techniques in the Delaware Basin, NM

Abstract

The main purpose of this study was to identify potential reservoirs in the 2nd and 3rd Bone Spring sandstones in the Todd/Apache areas, Delaware Basin. These sandstones consist of alternating carbonate and siliciclastic intervals that were deposited as submarine-fans systems within the Delaware basin during period of lowered sea level. The sandstones are composed of fine to very fine grains with porosity from 1% to 13% and low permeability from: 1×10-6 md to 2.5 md. At the beginning of this study, some parameters such as porosity and water saturation were used to define net thickness. However, the high water saturation values in some parts of the Todd/Apache areas did not match with the high productive wells. Based on that premise, a new approach that integrate stratigraphy, petrophysical attributes (Porosity, Deep Resistivity and Sandstone Volume) and production data using stochastic simulation technique was applied to capture the geological trend and to define potential reservoir in the Bone Spring Sandstones. Two main data sources were applied: wells with petrophysical evaluation and production data. The 55 wells with petrophysical evaluation were used to build the water saturation, porosity, sandstone volume and deep resistivity models using stochastic technique. The production data of 36 horizontal wells (25 with EUR and 11 with 180 Cumulative production data) was used to investigate the relationship between productions versus net thickness. Since there is no relationship between production and Sw in the Todd/Apache areas, only porosity, sandstone volume and deep resistivity attributes were used to define net thickness. A detail analysis of those attributes was made for each Bone Spring zone to identify the cutoff to be applied for the net thickness model. For Porosity a cutoff of > 5%, for Deep Resistivity a cutoff of < 30 ohm and for sandstone volume a cutoff of more than 50% was defined. With those cutoffs the carbonates and tight layers with less than 5% of porosity were removed from the model. Three net thickness maps (2nd Bone Spring Upper and Lower and 3rd Bone Spring Lower) were built to identify the areas where the three attributes match the cutoffs. A good relationship between production and net thickness was observed in the three zones: 2nd Bone Spring SS Upper and Lower and 3rd Bone Spring SS Lower. High net thickness is matching with the high productive well identifying zones with potential reservoir sandstones in the Todd/Apache areas.