Method of conducting in situ measurements of properties of a reservoir fluid

Abstract

When conducting in situ measurements etc. of the properties/parameters of a reservoir fluid, possibly in connection with analyses,use is made of a measuring instrument/apparatus-containing casing ( 7 ) at the upstream end of a drill string ( 4 ), which casing has a combined inlet/outlet facing the hydrocarbon-containing layer ( 2 ) of the reservoir and is in fluid communication with the bore of the drill string ( 4 ), in which is disposed a reciprocally sliding piston (17), the top of which—opposite the side for inflow of reservoir fluid (RF)—may be acted on by pressure through a pressurisable fluid (water or N 2 ) in order, on completion of the measurements, to force the reservoir fluid (RF) previously accommodated in the bore of the drill string back into the oil-containing layer of the reservoir. By so doing, a considerably capacity for accommodation of fluid is made available, represented by a drill string ( 4 ) upstream of a given point (the piston), with possibilities for return to source of an enormous volume of fluid. This is highly suited for subsea measuring apparatuses/instruments that—in order to give results with a very high degree of accuracy—require very large flow rates of test fluid.

1 . A method of conducting in situ measurements of properties of reservoir fluid by means of measuring instruments/apparatuses enclosed in a casing ( 7 ) connected to the outer, free end of a tubular string ( 4 ) that is movable in a wellbore/well ( 3 ) extending at least down to the hydrocarbon-containing layer ( 2 ) of the reservoir, where the inherent pressure of the reservoir fluid (the reservoir pressure) ensures the inflow of reservoir fluid into the instrument/apparatus casing ( 7 ) through an inlet ( 8 ), or possibly a combined inlet/outlet, and where signals that are generated electronically on the basis of measurements obtained in situ are passed on to the surface position, possibly for further analysis, charactarised in that measurements are initiated with the instrument/apparatus casing ( 7 ) in said in situ position and in fluid communication with the drill string ( 4 ), e.g. flow and/or volume measurements of the type that—in order to achieve measurement results with a high degree of accuracy—require a substantial volume of fluid, normally in the form of a multiphase fluid to pass through a passage with a given cross section in the respective measuring instrument/apparatus, which substantial volume of fluid in the form of reservoir fluid downstream of the respective measuring instrument/apparatus, referred to the direction of flow, is led from said instrument/apparatus casing ( 7 ) into the drill string ( 4 ) that is in fluid communication with same, again while utilising the inherent pressure of the reservoir fluid, the drill string ( 4 ) in use exhibiting such longitudinal extent and cross section of bore as enables it to accommodate a substantial volume of reservoir fluid that has flowed through the respective measuring instrument/apparatus for measurement purposes, and that a piston that may reciprocate freely in the bore of the drill string ( 4 ) and may be acted on from both sides by compressed fluid, is positioned so as to start in its upstream position at the start of the measuring operations, which position is immediately downstream of the instrument/apparatus casing, by means of reservoir fluid flowing into the bore of the drill string, which fluid has passed through said in situ measuring instrument/apparatus, is forced in the direction away from the instrument/apparatus casing ( 7 ) by the inherent pressure of this fluid, the downstream fluid is pressurised at the close of the measuring operation in order to reverse the direction of travel of the piston, the in the downstream direction displaced piston forcing the reservoir fluid admitted into the drill string out again into the hydrocarbon-containing layer ( 2 ), in a manner that is known per se.  
     
     
         2 . A method according to  claim 1 , characterised in that the drill string ( 4 ) is closed off by a valve arrangement ( 14 ) at its upper end when it has been filled with reservoir fluid that has passed through a measuring apparatus in the casing ( 7 ) in the hydrocarbon-containing layer ( 2 ) of the reservoir.  
     
     
         3 . A method according to  claim 1  or  2 , characterised in that trace elements are added to the reservoir fluid that is introduced into the drill string, from a trace element feeder disposed in the casing ( 7 ).  
     
     
         4 . A method according to  claim 1 , characterised in that—in an initial operation—mud/drill fluid in the drill string ( 4 ) on the upstream side of the piston (referred to the bottom of the well) is forced out into the annulus by said water/N 2  in the drill string ( 4 ) on the opposite side of the piston (downstream side), whereupon the bore of the drill string is ready to accommodate the reservoir fluid as it enters after having passed through a measuring apparatus for flow and volume measurements in the casing ( 7 ).  
     
     
         5 . A method according to  claim 1 , characterised in that the piston is brought to a halt in its upward movement in the drill string ( 4 ) by means of an internally thereof positioned seat/stop ( 18 ) with a through opening, against which seat the piston abuts and which seat is placed at a significant distance downstream of the apparatus/instrument casing ( 7 ).