US2323556A - Method and apparatus for determining effective porosity - Google Patents

Description

July 6, 9 E. o. MATTOCKS METHOD AND APPARATUS FOR DETERMINING EFFECTIVE POROSITY Filed NOV.. 29 1940 J in W s H d m f H H 4 n n R0 E J W mm m Q W w W 1% M W M mo 5 3 W m E M m a W N v w 9 v0 W H m 5 m m 2 1 V0 m M 3 W W m QT N. k m. 9 2 m h wmwxumozbw mm W 0F Q22 8 w om mm 11 MEUIHEOEE s5ou 7 0k mm mm mm mm 8 Patented July 6, 1943 'METHOD AND APPARATUS FOR DETERMIN- ING EFFECTIVE POROSITY I Elmer 0. Matt'ocks, Bartlesville, kla., asslgnor to Phillips Petroleum Company, a corporation of Delaware ApplicatiomNovember 29, 1940, Serial No. 367,855

'7 Claims.

This invention relates to an improved method and apparatus for determining the effective porosity of various solids, such as formation cores and other porous materials.

In drilling a hydrocarbon oil or gas well, it is common practice to obtain cores of the formation above or in the zone where hydrocarbon oil and/or gas are found. Such cores are obtained by the general methods employed in coring and having been obtained, various tests are made thereon to ascertain the productive value of the formation represented by the cores. One of the important characteristics of the core is its pore spaces, as any hydrocarbon fluids that may be present incores are contained in these spaces. The connected pore spaces are of prime importance in recovering oil or gas from a reservoir because the hydrocarbon fluids flow through these pores to the well bore. A knowledge of the size and extent of pore space is needed for determining the amounts of fluids which may be recovered from the reservoir and for determining the effects of water encroachment which is common in particular reservoirs. A study of the cores aids in estimating proper rates of withdrawal of fluid from the reservoir in order to obtain a maximum life for the producing oil wells and to recover the maximum amount of hydrocarbon fiuids at the most economical cost.

The ratio of the volume of connected pore "spaces to the total bulk volume of a formation 'is generally termed effective porosity and is commonly expressed as a percentage. The effectiveporosity of cores can be obtained by any one of several ways now commonly employed. One

method is to place the core with mercury in an air-tight container and draw a vacuum on the core by withdrawing mercury from the container.

This removes the air from the pores of the core.

' Before the volume of air thus withdrawn from the pores. can be measured, the pressure of that trapped air must be adjusted to atmospheric pressure. This requires the introduction again of mercury into the container. This mercury generally covers the core, and since pore space in the core is under a vacuum, mercury will enter the pores during the action of equalizing the pressure of, the trapped air to atmospheric conditions. The core cannot be used for additional tests unless the mercury is first removed from it. The removal of this mercury is a hazardous procedure; hence, the cores are discarded after a single test.

Porosity measurements are made generally on pieces cut from cores and the test specimens are usually relatively uniform in size and shape. The

data thus obtained from small pieces of core are used as representative samples of considerably larger sections. While this method has decided limitations, the results are generally representative and are usable for uniform or nearly uniform formations. In the case of formations, such as limestones and dolomites where the porosity varies widely over the length of the core, considerable error may result from using small sections of the core as representative of the formation. In this type of non-uniform formation, porosity tests should be made on relatively larger sections of the core. To accomplish this by the present known methods would require a large bulky piece of equipment which could not be used with the same degree of accuracy in testing smaller pieces of core. 0

My invention permits the determination of effective porosities of large, as well as small sections of cores, using the same apparatus with a minimum of operating technique and with the same degree of accuracy. The practice of my invention does not impair individual cores in any manner, and it is possible to use the same core for purposes other than porosity determination or to make any desired number of porosity tests.

This invention has for its primary object, the provision of an improved method and apparatus for measuring volumes of a porous solid for the purpose of determining the effective porosity of that solid.

Another object of this invention is to provide a method and apparatus for determining the volume of connected pore spaces within the cores of rock formation or other porous solids.

A still further object of this invention is to provide a method and apparatus for determining the effective porosity of both large and small cores, using the same apparatus with a minimum of operating technique to obtain results with the same degree of accuracy and for making any number of porosity determinations without impairing the core for further test purposes.

These and additional objects and advantages will be apparent to persons skilled in the art by reference to the following description and anriexed drawing which is an elevation view of the apparatus of my invention.

Referring to the drawing, an open-ended core container of any desired size is designated by numeral l. A holder or vice 2 has a plate 3 and is so constructed that by actuating a. screw 4, core container I makes an air-tight seal with plate 3 and communicates with valves 5 and 8, and a pressure gauge 1 through an outlet 8. Valve 5 communicates with a valve 9 and drying tube I8 Y through conduit I I for supplying air or any other desired gas, and also with a valve I 2 and a deadweight tester (not shown) through a conduit I3. A conduit I4 connects valve 8 with a water mathe mercury reaches the top 01' burette I8, valves 7 nometer I through a valve I8,'with a mercury manometer." which serves only as a pressure relief device, with a calibrated burette I8 through a 3-way valve I8, and with a manifold or header Header also communicates with a plurality of expansion bottles 21, 28, 29, 38 and 3I of known volume through valves 32, 33, 34, 98 and 38, respectively. A mercury leveling bulb 31 connects with a burette I8 through a flexible conduit 38,

as allowed by a valve 39. A second mercury leveling bulb 48 connects with mercury manometer 24 through a conduit H, as allowed by a pinch valve 42. A pair of stands 43 support the I mercury leveling bulbs 31 and 40., A core section 44 is indicated in core container I. For ease oi operation, it is desirable to choose core containers which are as near the size suitable for the core to be tested as possible.

The effective porosity of a core is theratio ,of.

the volume of connected pore spaces to thebulk volume of the core, as expressed in the percent in the formula,

wherein V is the volume of the connected pore spaces, V1: is the bulk volume of the core as defined by its external dimensions, and Va is the combined volume of the nonporous materials and the nonconnected pore spaces. It is obvious that Vp=Vb-Vn. The bulk volume of the core Vb may be ascertained by any one of the usual methods. The combined volume of the nonporous materials and the nonconnected pore spaces Vn is obtained by practicing my invention and the above equation is then solved to find the percent eifective porosity Vp.

To determine the value of Vn for core 44, the core is deposited in core container I, which'is placed in vice 2; and by operating screw 4, an airtight seal is made with'plate 3. Core container I is thus placed in communication with outlet 8, valves 5 and 8, and gauge 1. Valve 8 is closed, valve 5 is opened, valve I2 is closed, and air enters score container I through air supply Effective porosity i X 100= X 100 conduit II, drying tube III and valve 9. The air mitted into burette I8 by opening valve. When 39 and I9 are closed.- Valves 32, 33', 34, 35 and 38 are then opened and the plurality of expansion bottles represented'by 21, 28, 29, 38 and 3I are I connected into manifold 28. Vacuumpump 23 is then connected into the system through conduit 28 and 3-way valve 23 is opened, thereby permitting manifold 28 and mercury manometer 24 to communicate with the vacuum pump 28. By positioning leveling bulb 48 so that the open or atmospheric side of the manometer mospheric pressure, the zero point being on the closed side next to valve 23, it is possible to read the absolute pressure in the expansion bottles. The pressure in these bottles during evacuation is observed on manometer. 24. After the bottles are evacuated, valves 32, 33, 34, "and 38 are closed; vacuum pump 25 is disconnected from the system; and mercury manometer 24 is connected into the manifold 20 by operating 3-way valve 23. Valves 2I and 22 are then opened, adjusting the manifold 20 to atmospheric pressure. After a short interval of time, valve 22 1s closed and the apparatus is fully conditioned to receive the air that has been previously introduced into container I. The size of the expansion bottles to be used is dependent upon the size of core conpressure in container I is measured by pressure gauge 1 or in any other manner well known in the art. Air at a known superatmospheric pressure is admitted into core container I and valves 9 and 5 are then closed, trapping the air within core container I. Before expanding and measuring the air entrapped in the core container, it is necessary to condition that part of the apparatus in which expansion is to take place. This is accomplished by opening valves 22, 2|, I9 and I8, subjecting manifold 20, calibrated burette I8, mercury manometer I1 and water manometer I5 to atmospheric pressure. In the step outlined in the preceding sentence, 3-way valve I9 is open to connect burette I8 to the system. Valves 23,

32, 33, 34, 35 and 38 remain; closed during this operation. Valves I8, I9, 2i and 22 are then closed. Valve I9 is next opened to the atmosphere and mercury from leveling bulb 31 15 adtainer I and the size of core section 44 to be tested. Assume that bottle 21 is' of suitable size to hold part of the air to be expanded from core container I. Valve 32 is then opened and valve 8 slightly opened, allowing the air to expand from container I into bottle 21. The pressure on mercury manometer 24 and pressure gauge 1 is observed at all times and if appreciable pressure still exists within container I after expansion into bottle 21, valve 33 is opened and the air is allowed to further expand to bottle 28. If

the indicated pressure on gauge 1 is now almost atmospheric, but a slightly elevated pressure still exists within the system, as'shown on manometer 24, valve I9 is opened, connecting burette I8 into the system. By lowering mercury leveling bulb 31 and opening valve 39 a small amount, the pressure within the system can be reduced to approximately that of the atmosphere. At this time, valve I6 is openedand water manometer I5 1 is connected into the system. This manometer will indicate a very slight diflerential between the pressure within the apparatus and that of the atmosphere. Further adjustment of the height of the mercury column in burette I8 will make the pressure within the apparatus equal to that of the atmosphere.

The volume of air that had been admitted into core container I at superatmospheric pressure, designated as P5, is equivalent to the internal volume of bottles 21 and 28 plus the volume of air in burette I8, after expansion to atmospheric pressure, designated as Pa. At superatmospheric pressure, this volume of air represented the difference between the internal volume of the empty core container plus the volume of the appurtenances and Vn. The air admitted into the core container under pressure is expanded for convenience in measuring, and its volume at atmospheric pressure may then be designated as V2.

It is essential to my calculations to know the volume of air at atmospheric pressure, designated as Vi, that can be placed in the container I and the appurtenances at the aforementioned superatmospheric pressure with the core 44 removed from the container. The difference between V1 and V2 represents the volume of nonporous mareads at- Search Roon terials of the core and the nonconnected pore spaces; or I may write mathematically I) ejonv2) v.

V! may also be determined by following the procedure outlined with respect to determine V2, if desired.

In the foregoing calculations and measurements, necessary corrections must be made for indicating means connected to the receptacle, deviation from the ideal gas laws and for changes means for transmitting gas into the receptacle in temperature and pressure. at a known pressure above said predetermined From the foregoing, it is believed that the pressure, gas receiving means of variable volumethod and apparatus for practicing my instant metric capacity connected to the receptacle, and invention will be readily comprehended by per- 15 means associated with the gas receiving means sons skilled in the art. It is to be clearly underand controlling the pressure within the gas restood. however, that various changes in the apceiving means without loss of gas transmitted paratus herewith shown and described as a prethereinto. fer ed E b iment f y invention and in the 5. In apparatus for determining the volume of modes of operation outlined above may be re- 20 connected pore spaces in a porous body, the comsortcd to w t departing from e pirit Of bination comprising a receptacle for containing the invention as defined by the appended claims. the body at atmospheric pressure, pressure indi- I claim: eating means connected to the receptacle, means 1. In a method of determining the volume of for transmitting gas into the receptacle at a connected pore spaces in a porous body, he S ps :5 known superatmospheric pressure, gas receiving comprising placing the body in a closed zone at a means of variable volumetric capacity connected kn wn p e, introducing gas at a predeterto the receptacle, and means for lowering the mined Pressure that is above said known pressure pressure within the gas receiving means to a point into the closed zone, placing the closed zone in below atmospheric pressure. communication with a second closed zone which :m 6. In apparatus for determining the effective is at a pressure below said known pressure, exporosity of a porous body, the combination companding the gas from the first closed zone into prising a receptacle for containing the body at a the second closed zone until the pressure in both predetermined pressure, pressure indicating zones is substantially that of the above menmeans connected to the receptacle, means for tioned known pressure, and thereupon ascertain- 35 transmitting gas into the receptacle at a known ing the volume occupied by the gas in the second pressure above said predetermined pressure, a zone. manifold connected to the receptacle, gas receiv- 2. In a method of determining the volume of ing means of variable volumetric capacity conconnected pore spaces in a porous body, the steps nected to the manifold, and means for lowering comprising placing the body in a closed zone at 40 the pressure within the gas receiving means to a atmospheric pressure, introducing gas at known superatmospheric pressure into the closed zone, placing the closed zone in communication with a second closed zone which is at a pressure below atmospheric pressure, expanding the gas from the first closed zone into the second closed zone until the pressure in both zones is substantially atmospheric, and thereupon ascertaining the volume occupied by the gas in the second zone.

3. In a method of determining the effective porosity of a formation core, the steps comprising placing the core in a closed zone at atmospheric pressure, introducing dry gas at known superatmospheric pressure into the closed zone, placing the closed zone in communication with a second closed zone which is substantially evacpoint below atmospheric pressure.

'7. In apparatus for determining the effective porosity of a formation core, the combination comprising a receptacle for containing the core at atmospheric pressure, pressur indicating means connected to the receptacle, means for transmitting substantially dry gas into the receptacle at a known superatmospherie pressure, a manifold connected to the receptacle, gas receiving means connected to the manifold and including a plurality of containers of predetermined volumetric capacity and valve means for selectively placing the container in communication with the manifold, and mean for substantially evacuating the containers.

ELMER O. MATTOCKS.

CERTIFICATE OF CORRECTION. Patent No. 2,525,556. July 6', 19m.

ELMER 0 HAT'I'OCKS It is herebycertified that error appears in the printed specification of the above mgmb ered patent requiring correction as follows: Page 5, first column, line ii, in the formula, for

read s s and that the said Letters Patent shonld be read with this correction therein that the same may conform to the record of the cese in the Patent Office.

Signed and sealed this 26th day of October, A. D. 1915.

- i Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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