Critical Gas Rate Correlation for Compositional Reservoirs
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Solution Overview
Problem
Predicting critical gas rate in oil and gas reservoirs is challenging, especially in natural fracture gas and volatile oil reservoirs, due to uncertainties in fluid flow behavior and limited data on gas-water relative permeabilities, leading to potential well production losses.
Innovation Solution
A computer-implemented method using a power law correlation of Gas Liquid Ratio (GLR) vs. Water Gas Ratio (WGR) to estimate unstable flow conditions, adjusting relative permeabilities and field constants to match separator data, and employing diagnostic plots to identify critical gas rates without requiring initial relative permeability knowledge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the Turner equation is used to estimate critical gas rate, then the prediction is simple and widely applicable, but it overestimates volumes and fails for compositional fluid reservoirs
Solution Approach 1:
The patent transforms the Turner equation parameters by introducing compositional fluid properties (GLR, WGR, relative permeabilities) to create a modified correlation that adapts to different reservoir types, thereby maintaining simplicity while improving accuracy for compositional fluids
Solution Approach 2:
The patent creates a power law correlation that copies the functional form of the Turner equation but replaces its constants with composition-dependent parameters derived from separator test data, enabling accurate prediction for both conventional and compositional reservoirs
2Measurement precision
If relative permeability data is obtained through core flooding experiments, then accurate near wellbore relative permeabilities are achieved, but the process is time-consuming and expensive
Solution Approach 1:
The patent uses separator test data (GLR, WGR, gas/oil/water rates) as an intermediary to infer near wellbore relative permeabilities, avoiding the need for direct core flooding experiments while still obtaining composition-specific permeability information
Solution Approach 2:
The patent replaces the mechanical core flooding experiment system with a computational approach that uses readily available separator test data and power law correlations to determine relative permeability relationships
3Measurement precision
If separator test data is collected and analyzed using power law correlation, then accurate critical gas rate prediction is achieved, but the workflow becomes more complex
Solution Approach 1:
The patent develops a universal power law correlation framework that handles both conventional and compositional fluid reservoirs through a single methodology, using separator test data to determine composition-specific parameters without requiring different approaches
Data Source
AI summary
Systems and methods include a computer-implemented method for adjusting a critical line for a wellbore. A separator test is performed for a well that is flowing at unstable conditions. In response to determining that a Turner equation does not predict the critical line for the wellbore, a water gas ratio (WGR) and a gas liquid ratio (GLR) are determined using gas, oil, and water rates from a separator of the well. When a gas relative permeability (Krg), an oil relative permeability (Kro), and a water relative permeability (Krw) are available, Krw and Kro are adjusted until they match the separator data at critical conditions in a GLR-WGR log-log plot for the well. Otherwise, a field constant Cfield is adjusted until it matches the separator data at critical conditions in a GLR-WGR log-log plot. The critical line is adjusted based on the WGR.