Method for determining formation pressure
AssigneeLouisiana State University and Agricultural and Mechanical College
InventorRobert Desbrandes
Life of this patent
Estimating the term…
Abstract
A method for accurately determining the formation pressure of earth formans. Formation measurements are made with by use of a novel downhole tool which allows drilling mud to enter the tool in such a way that decompression of drilling mud is controlled so that the pressure in the borehole is allowed to fall only slightly below the formation pressure. The drawdown of mud into the tool is then stopped and the pressure is allowed to stabilize at the formation pressure. The measurement is completed in a matter of a few minutes as opposed to hours, or even days, as required by more conventional techniques.
Claims16
A method for testing subsurface formations from a borehole containing compressed drilling fluid, which method comprises:
- (a) positioning a drillstem down hole test tool down a borehole adjacent to the formation to be tested, said test tool containing:
- (i) an entry port, (ii) a chamber of known volume, (iii) a means for controlling the flow rate of the drilling fluid into the test tool, and (iv) a pressure measuring means;
- (b) utilizing at least one packer to isolate an interval of borehole by expanding the packer and sealing the annular space between the test tool and the bore- hole;
- (c) effectively controlling the flow rate of drilling fluid into the chamber of the test tool so that substantial instantaneous decompression of the drilling fluid does not occur;
- (d) measuring chamber pressure at constant time intervals between about 0.1 and 10 seconds;
- (e) stopping the flow rate of drilling mud into the chamber of the test tool when the pressure drops below the formation pressure;
- (f) letting the pressure stabilize, which stabilized pressure will be an indication of the formation pressure.
A method for testing subsurface formations from a borehole containing compressed mud, wherein said formations have a permeability in the range of about 0.01 to 5 millidarcies, which method comprises:
- (a) positioning a drillstem down hole test tool down a borehole adjacent to the formation to be tested, said test tool for making multiple tests before being raised to the surface, which tool contains:
- (i) an entry port, (ii) a chamber of known volume, (iii) a means for controlling the flow rate of the mud into the test tool in the range of about 0.4 in.sup.3 /min to about 40 in.sup.3 /min, and (iv) a pressure measuring means;
- (b) utilizing at least one packer to isolate an interval of borehole by expanding the packer and sealing the annular space between the test tool and the bore- hole;
- (c) effectively controlling the flow rate of mud into the chamber of the test tool so that substantial instantaneous decompression of the drilling fluid does not occur;
- and
- (d) measuring chamber pressure at constant time intervals between about 0.1 and 10 seconds:
- (e) stopping the flow rate of drilling mud into the chamber of the test tool when the pressure drops below the formation pressure;
- (f) letting the pressure in the borehole interval stabilize, said stabilized pressure being the formation pressure.
Dependencies are inferred from the claim text.