Production data analysis and reservoir simulation of the Eagle Ford shale are very challenging due to the complex characteristics of the reservoir and the fluids. Eagle Ford reservoir complexity is expressed in the enormous vertical and horizontal petro-physical heterogeneity, stress-sensitive permeability, and existence of multi-scale natural fracture and fault systems. This complexity makes the prediction of the geometry and conductivity of the hydraulic fracture resulting from the stimulation process rather challenging. On the other hand, reservoir fluid complexity is demonstrated in multi-phase flow, liquid loading in the wellbore, condensate banking, etc. Based on this complexity, 3D reservoir modeling and numerical simulation have the relative advantage of addressing irregular fracture geometry, variable SRV, and multi-phase flow aspects. The South Texas Asset Team at Pioneer Natural Resources is establishing a workflow for dynamic reservoir modeling that can integrate all reservoir/wellbore parameters (formation evaluation, drilling, completion, stimulation, pre-/post-fracture surveillance, and well performance data) in order to address key questions relating to field development; such as depletion efficiency, drainage area, wells interference, and condensate banking effects. In this paper, a case study is presented to demonstrate the integration of various measurements and surveillance data to build a variable SRV reservoir model. The variable SRV model described here has the following building blocks: 1) Formation evaluation: included all the reservoir characterization data derived from logs and 3D seismic inversions and structural attributes. 2) Surveillance data integration: microseismic data (backbone for this work) are integrated with chemical and radioactive tracer logs. 3) Well performance data integration: Production data is used to determine different flow regimes during the well history and to set bounds for stimulation parameters, such as fracture half-length and permeability ( √ ). 4) Numerical simulation: Micro-seismic attributes (density and magnitude) are converted to a permeability model after being calibrated with tracer logs and production flow regime parameters ( √ ). PVT data is matched against an Equation of State (EOS) and input into the model. Production data history matching, sensitivity and forecasting indicate the following: a) The SRV created by fracture stimulation has permeability fading away from the wellbore; b) Fracture geometry is variable and results in an irregular drainage area along the lateral; C) Onset of condensate banking near wellbore and along the fracture(s) can occur within the first year of production if draw down is not managed properly.
One of the greatest technical challenges in the development of gas and oil unconventional reservoirs is the optimization of the horizontal and vertical well spacing. Drainage volume and depletion efficiency around a horizontal lateral are the most important factors in the well spacing decision-making process. Drainage volume around a horizontal well is dependent on the stimulation design/execution and on the petrophysical and textural properties of the reservoir in the near wellbore area. Surveillance data acquired during stimulation (microseismic monitoring and tracers data) and during production (well pressure & interference) are routinely used to estimate the expected drainage area around wellbores. These surveillance measurements have numerous technical and operational limitations such as availability and location of monitoring well, accuracy of velocity model, detection of radioactive tracers away from wellbore, temperature limitation for down hole pressure gauges, etc.In this study, we show a workflow that can reduce the level of uncertainty in estimating drainage area and depletion zones around wellbores. The workflow consists of: 1) Converting microseismic events into a density volume. 2) Conditioning the density volume by adding surface seismic attributes in zones where higher permeability is to be expected. 3) Conversion of the conditioned density volumes to permeability using rate transient and stimulation drivers such chemical tracers and production logs. 4) The 3D permeability model is fed into a reservoir simulator to match pressure and production history.Microseismic density volumes are predicted in adjacent boreholes at varying distances from the actual wellbore to create a multiwell density volume using surface seismic attributes and rock property estimates. These volumes are taken into a reservoir simulator to predict expected ultimate recovery, recovery factor and the stimulated area per well.
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