Gravity Measurement for Reservoir Fluid Front Tracking
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Solution Overview
Problem
Current gravity measurement tools face challenges in accurately and efficiently determining the depth and geometrical properties of gravitational anomalies in subterranean formations, particularly in monitoring changes in subterranean reservoirs, due to high computational costs and non-uniqueness of solutions in inverse gravity problems.
Innovation Solution
A method involving time-lapse measurements of the vertical component of gravitational force in a wellbore to determine the depth of a gravity anomaly, using a non-linear equation to derive parameters such as the distance and height of a density anomaly, allowing for fast and low-cost estimation of fluid front location and thickness, even in complex geometries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inverse gravity problem solving methods are used to determine depth and geometrical properties of gravitational anomalies, then measurement precision is improved, but computational cost increases significantly
Solution Approach 1:
The patent segments the complex inverse gravity problem into distinct depth intervals by identifying sign changes in gravity differences between adjacent measurement depths. This divides the continuous inversion problem into discrete segments that can be processed independently and more efficiently, reducing overall computational burden while maintaining precision in determining anomaly depths.
Solution Approach 2:
Instead of directly solving the traditional inverse gravity problem through computationally intensive optimization, the patent inverts the approach by calculating gravity differences between adjacent depths and identifying where these differences change sign. This indirect method provides an efficient pathway to determine anomaly depths without requiring full-scale iterative inversion computations.
2Measurement precision
If comprehensive inversion methods are applied to determine all parameters of gravitational anomalies, then measurement precision is improved, but the solution becomes non-unique
Solution Approach 1:
By segmenting the problem into depth-specific gravity difference analysis, the patent identifies unique depth locations through sign changes without requiring full inversion of all anomaly parameters simultaneously. This segmentation provides reliable depth determination while avoiding the non-uniqueness issue that plagues comprehensive inversion methods.
Solution Approach 2:
The patent extracts and focuses specifically on the depth parameter by analyzing gravity differences between adjacent measurement depths. This extraction of the depth determination problem from the full set of inversion parameters provides a unique and reliable solution for depth location without needing to resolve all other anomaly characteristics, thereby avoiding solution non-uniqueness.
3Measurement precision
If detailed geometrical properties of density anomalies are determined through inversion, then measurement precision is improved, but processing time increases
Solution Approach 1:
The patent applies an inverted approach by calculating gravity differences and identifying sign changes rather than performing time-consuming forward modeling and iterative inversion. This provides rapid determination of fluid front location and anomaly depth with sufficient precision for monitoring applications, significantly reducing processing time.
Solution Approach 2:
The patent performs partial inversion by focusing only on determining depth locations through gravity difference sign changes, rather than computing all geometrical properties of the anomalies. This partial action provides the essential information needed for fluid front tracking while avoiding the excessive processing time required for complete geometrical characterization.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient monitoring of fluid front movement and density anomalies with reduced computational costs, providing accurate estimates of fluid front location and thickness, and serving as a priori information for other inversion methods, enhancing the detection of fluid migration and fingering between injector and producer wells.
Implementation Method 1
obtain a time-lapse measurement of at least a vertical component of the gravitational force in the wellbore
Implementation Method 2
The gravity sensors are fiber optic interferometry devices, which measure a velocity of a free falling mass by determining, with respect to time, interference fringe frequency of a light beam split between a first path having a length corresponding to the position of the free falling mass
Implementation Method 3
measure a velocity of a free falling mass by determining, with respect to time, interference fringe frequency of a light beam
Data Source
AI summary
A method of performing gravity surveys in a wellbore is described including performing a time-lapse measurement in a monitoring well in the vicinity of injector wellbores, determining a depth for which the difference of the time lapse measurements changes sign or crosses zero as depth of the anomaly; and using said measurements at other depth points to further determine one or more parameters relating to the location and/or size of a density anomaly caused by injecting fluids through said injector wellbores, thus enabling the sweep of an injected fluid including the occurrence of fingering in the formation.