Method and tool for evaluating a geological formation

Abstract

A method of evaluating a geological formation ( 20 ) of non-homogeneous porosity and permeability, particularly in exploration for hydrocarbon fluids, comprising the steps of: (a) inserting a formation evaluation tool ( 30 ) into a borehole ( 10 ) to a location ( 10 a ) within the geological formation ( 20 ); (b) setting the formation evaluation tool ( 30 ) into position isolating interval(s) of the borehole ( 10 ) with a packer arrangement ( 50 ) forming portion of the formation evaluation tool ( 30 ), for sample evaluation for said interval(s); (c) extracting representative samples of formation fluid from the location within the geological formation ( 20 ) for evaluation under downhole conditions using sampling means ( 32 a, 52 b, 54 b ) operative to extract formation fluid samples over a range of porosity and permeability encountered within the geological formation ( 20 ); and (d) analysing the formation fluid samples and measuring formation ( 20 ) permeability. A formation evaluation tool ( 30 ) for practising the method, and including an packer arrangement ( 50 ) for isolating intervals of the borehole ( 10 ) for sample acquisition and evaluation, is also disclosed. The method and tool ( 30 ) are particularly suited to geological formations comprising complex carbonate rocks such as mudstones, Wackestone, Packstone, Boundstone and crystalline carbonate rocks which typically include features such as vugs and fractures.

1 - 17 . (canceled) 
     
     
         18 . A method of evaluating a geological formation of non-homogeneous porosity and permeability comprising the steps of:
 (a) inserting a formation evaluation tool into a borehole by wireline, after drilling of the borehole, to a location within the geological formation;   (b) setting the formation evaluation tool into position isolating interval(s) of the borehole with a packer arrangement forming portion of the formation evaluation tool, for sample evaluation for said interval(s);   (c) extracting representative samples of formation fluid from the location within the geological formation for evaluation under downhole conditions using sampling means for extracting formation fluid samples over a range of porosity and permeability encountered within the geological formation; and   (d) analysing the formation fluid samples and measuring formation permeability, wherein said packer arrangement is a dual or straddle packer arrangement comprising a plurality of spaced apart packers, each packer comprising sealing elements for isolating sampling interval(s) within said borehole enabling extraction of samples for acquisition of data for formation evaluation through at least one sampling port located between said sealing elements of a packer.   
     
     
         19 . A method of  claim 18  wherein said geological formation includes a feature selected from the group consisting of vugs, fractures, variable diameter pores and moldic pores. 
     
     
         20 . A method of  claim 18  wherein the sampling port is set back from a wall of the borehole such that a space enabling sample draw down is disposed between said sealing elements isolating a sampling interval. 
     
     
         21 . A method of  claim 18  wherein said data is used to evaluate vertical continuity of said geological formation. 
     
     
         22 . A method of  claim 18  wherein measuring differential pressure between packers spaced a fixed known distance apart allows determination of the density of fluids present at a location within said geological formation taking downhole conditions into account. 
     
     
         23 . A method of  claim 18  comprising the step of identifying the representative nature of a formation fluid sample, once extracted by the sampling means, by monitoring a signal from at least one sensor, and preferably a plurality of sensors, included within the formation evaluation tool. 
     
     
         24 . A method of  claim 18 , wherein said sealing elements are inflatable. 
     
     
         25 . A formation evaluation tool to be inserted into a borehole by wireline, after drilling of the borehole, for evaluating a geological formation of non-homogeneous porosity and permeability and comprising a packer arrangement for isolating interval(s) of said borehole for evaluation; and sampling means for extracting formation fluid samples from said interval(s) for evaluation samples under downhole conditions wherein said sampling means operates to obtain formation fluid samples over a range of porosity and permeability encountered within the geological formation enabling sample analysis and measurement of permeability, wherein said packer arrangement is a dual or straddle packer arrangement comprising a plurality of spaced apart packers, each packer comprising sealing elements for isolating sampling interval(s) within said borehole enabling extraction of samples for acquisition of data for formation evaluation through at least one sampling port located between said sealing elements of a packer. 
     
     
         26 . A formation evaluation tool of  claim 25  wherein the sampling port is set back from a wall of the borehole such that a space enabling sample draw down is disposed between said sealing elements isolating a sampling interval. 
     
     
         27 . A formation evaluation tool of  claim 25  comprising a tubular string including a number of tubular subs. 
     
     
         28 . A formation evaluation tool of  claim 25 , wherein said sealing elements are inflatable. 
     
     
         29 . A formation evaluation tool of  claim 25 , comprising at least one sensor for producing signals to be monitored to identify that formation fluid samples are representative. 
     
     
         30 . A formation evaluation tool of  claim 29  comprising a plurality of sensors including at least two sensors selected from the group consisting of conductivity, resistivity, temperature, flow-rate, pressure and density sensors. 
     
     
         31 . A formation evaluation tool of  claim 29  comprising a tubular string including a number of tubular subs wherein a sub of said tubular string accommodates the sensor(s). 
     
     
         32 . A formation evaluation tool of  claim 31  wherein each said packer comprises a tubular mandrel with a longitudinal axis and a housing slidable relative to said mandrel which allows accommodation of inflatable sealing elements, each inflatable sealing element being substantially concentrically disposed about, and sealingly attached to, the tubular mandrel and communicable with a source of pressurised fluid to inflate each sealing element such that, when inflated, the sealing elements extend radially outward toward a borehole wall to achieve sealing wherein a sample port is located in a portion of the housing low or very low expansion ratio relative to expansion ratio of the sealing elements. 
     
     
         33 . A method of evaluating a geological formation of non-homogeneous porosity and permeability comprising the step of analysing data from samples of formation fluids extracted from the geological formation according to the following steps:
 (a) inserting a formation evaluation tool into a borehole by wireline, after drilling of the borehole, to a location within the geological formation;   (b) setting the formation evaluation tool into position isolating interval(s) of the borehole with a packer arrangement forming portion of the formation evaluation tool, for sample evaluation for said interval(s); and   (c) extracting representative samples of formation fluid from the location within the geological formation for evaluation under downhole conditions using sampling means for extracting formation fluid samples over a range of porosity and permeability encountered within the geological formation,   wherein said packer arrangement is a dual or straddle packer arrangement comprising a plurality of spaced apart packers, each packer comprising sealing elements for isolating sampling interval(s) within said borehole enabling extraction of samples for acquisition of data for formation evaluation through at least one sampling port located between said sealing elements of a packer.   
     
     
         34 . A method according to  claim 33  wherein the sampling port is set back from a wall of the borehole such that a space enabling sample draw down is disposed between said sealing elements isolating a sampling interval.