Method of assessing positional uncertainty in drilling a well
First Claim
1. A method of estimating positional uncertainty in drilling a well, comprising:
- supplying a first set of values representing a first three-dimensional uncertainty of the actual position of a drill bit with respect to the estimated position thereof;
supplying a second set of values representing a second three-dimensional uncertainty of the actual position of a geological feature with respect to the estimated position thereof;
combining the first and second sets of values to form a third set of values representing a third uncertainty of the position of the drill bit with respect to the geological feature;
calculating from the third uncertainty the probability that the drill bit reaches a predetermined position relative to the geological feature;
defining at least one geological target as a finite surface relative to the geological feature; and
correcting at least one value in the first set of values using information from a marker point whose relative position including positional uncertainty to the at least one geological target is at least partly known.
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Accused Products
Abstract
A method is provided for estimating the positional uncertainty in drilling a well such as an oil well. A first set of values is supplied representing a first three-dimensional uncertainty of the actual position of a drill bit with respect to the estimated position. A second set of values is supplied representing a second three-dimensional uncertainty of the actual position of a geological feature with respect to the estimated position thereof. For example, the first set of values relates to positional uncertainties because of the drilling procedure whereas the second set of uncertainties is associated with the obtaining and interpretation of seismic data. The first and second sets of values are combined to form a third set of values which represents a third uncertainty of the position of the drill bit with respect to the geological feature. A probability is then calculated from the third uncertainty and gives the probability that the drill bit will reach a predetermined position relative to the geological feature.
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Citations
20 Claims
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1. A method of estimating positional uncertainty in drilling a well, comprising:
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supplying a first set of values representing a first three-dimensional uncertainty of the actual position of a drill bit with respect to the estimated position thereof;
supplying a second set of values representing a second three-dimensional uncertainty of the actual position of a geological feature with respect to the estimated position thereof;
combining the first and second sets of values to form a third set of values representing a third uncertainty of the position of the drill bit with respect to the geological feature;
calculating from the third uncertainty the probability that the drill bit reaches a predetermined position relative to the geological feature;
defining at least one geological target as a finite surface relative to the geological feature; and
correcting at least one value in the first set of values using information from a marker point whose relative position including positional uncertainty to the at least one geological target is at least partly known. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
defining a plurality of geological targets along a drill path;
calculating the probability of the drill path intersecting each of the geological targets; and
deriving from the calculated probabilities the probability of the drill path staying within a corridor defined by the geological targets.
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8. The method of claim 1, further comprising the step of selecting a desired point of intersection of a drill path with the at least one geological target.
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9. The method of claim 8, further comprising the step of calculating the probability of the drill path intersecting the at least one geological target.
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10. The method of claim 9, wherein the at least one geological target is a polygon.
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11. The method of claim 10, wherein the at least one geological target is rectangular.
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12. The method of claim 10, further comprising the step of ascribing a maximum acceptable probability of the drill path missing the at least one geological target to each side of the polygon.
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13. The method of claim 1, further comprising the step of calculating the probability of the drill bit being at a predetermined distance from the at least one geological target.
14.The method of claim 1, wherein the marker point is the position of the drill bit during drilling when the drill bit penetrates a seismic reflector whose distance from the at least one geological target is at least partly known. -
14. The method of claim 1, wherein the at least one geological target is selected to coincide with a predetermined geological structure, wherein the marker point is disposed at the predetermined geological structure, and wherein the position of the predetermined geological structure is derived from a pilot well.
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15. The method of claim 1, further comprising the steps of:
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recalculating the probability of the drill path intersecting the at least one geological target after the step of correcting at least one value in the first set of values; and
changing the direction of the drill path if the probability of the drill path intersecting the at least one geological target is less than a predetermined value.
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16. The method of claim 1, wherein the marker point is observed during drilling using means disposed at or adjacent the drill bit.
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17. The method of claim 1, further comprising the step of defining a drill target as a sub-surface within the at least one geological target, and wherein a drill path is directed at a point within the drill target.
- 18. The method of claim 18, further comprising the step of calculating the probability that the drill path will intersect the at least one geological target.
Specification