GB2188352A - Core sampling equipment - Google Patents

Abstract

A core barrel comprises an inner chamber 2 and an outer chamber 1 connected by means of a swivel 12, the outer chamber 1 being rotatable and connectable at one end to a drill string and at the other end to a corehead 3, the inner chamber 2 being adapted to remain stationary in relation to the core and comprising a core catcher 4 at one end and a wireline fishing neck 10 at the other. The inner chamber 2 also comprises a socket 7 adapted for the reception of a wireline survey instrument 8 and apertures above the socket for the passage of mud. The core barrel is suitable for wireline deployment and recovery of both a surveying instrument 8, such as an MWD instrument, and the core. <IMAGE>

Description

SPECIFICATION Core sampling equipment The present invention relates to equipment for taking core samples.

While drilling a well it is often necessary to take a coresample, particularly in the reservoir rock of the pay zone. A core is an undisturbed sample of the formation required by the geologist and palaeontologistfor correlation and identification purposes, and by the reservoir engineerfor permeability and porosity studies and for oil and water saturation measurements. Cores are usually taken on exploration wells and early development wells.

Modern drilling is very destructive of the rocks penetrated so that the fragments which reach the surface in the drilling mud are incomplete and difficu It to interpret. For example, clay in the rock tends to become part of the mud and be lost, while fragments of different size, shape and densitytravel upwards with the mud at different speeds and so arrive at the surface at different times.

For this reason, special coring equipment has been designed.

Cores are taken with a core barrel, which consists of an outer and inner barrel. The outer barrel is a case which acts as protection for a thinner-walled inner tube. The two are connected by means of a bearing at the top of the innertube which, to avoid damageto the core, does not rotate. Circulation isthroughthe annulus between the two. Acore bit is attached to the bottom of the outer barrel. Coreheads are usually diamond, similar in design to a diamond bit, butwith a concentric hole through the face, the diameter of which is fractionally smaller than the inside diameter of the inner barrel. When the core barrel is rotated on the bottom the un-cut section of the formation passes through the centre of the bit and into the inner barrel where it is held by catchers.On completion of the core, the string is pulled from the hole, the inner barrel is removed, and the core is extracted hydraulically with a hand pump.

The procedure for tasking a core is basicallythe same asforordinary drilling, exceptthattheweight and rotary speed are more carefully controlled to ensure that the outer barrel will not buckle and break the core. Core barrels are made in multiples of 30ft (9.14m) and, depending on the type offormation, up to SOft (27.4m) of core can be cut in one run of a three-section barrel.

Orientated coring has recently become of interest because of the need to obtain further information about reservoir properties. An oriented core can provide information about fracture orientation, permeability and porosity in specific directions and bedding plane orientation. This information enables the results of possible treatments to be predicted more accurately.

A barrel used to cut an oriented core is slightly different from a conventional barrel in that the core catcher has three longitudinal scribing blades on the inside. These are placed atnon-equal angles around the perimeter such that when the core is recovered, it is not possible to confuse the scribe lines and hence the orientation.

Both conventional and orientated coring involve pulling the complete drillstring out of the hole in order to recoverthe core and nothing is known about the core until it is taken out of the hole.

In order to survey while orientated coring it has been the practice to use a surveying instrument known as a magnetic multishot in connection with the inner barrel. The magnetic multishot is usually placed in position at surface but can be run on wireline after the assembly has been run in hole.

Wireline operation is a known technique in which a tool or instrument is lowered down a borehole on a wire and subsequently recovered when its task is completed.

The magnetic multishot is a camera type tool and coring and circulation must stop for each surveyto take place under static conditions. It is generally programmed to take a survey every few minutes, e.g.

5 - 15 minutes. This greatly increases the time required to complete the operation. Furthermore, by stopping in the middle of operations, the likelihood of problems occurring may increase. The core may jam on re-starting. The string may become stuck and if there is any deviation in the hole the chances of sticking are increased.

No information is available until the magnetic multishot has been withdrawn from the hole and the surveys processed. Whilst the magnetic multishot may be on wireline and therefore removable without withdrawing the drill string, the same does not apply to the core which, as before, can be recovered only by pulling the drill string out of the hole.

We have now devised a core barrel suitable for wireline deployment and recovery of both surveying instrument and'core.

Thus according to the present invention there is provided a core barrel comprising an inner and an outer chamber, the outer chamber being rotatable and connectable at one end to a drill string and at the other end to a corehead, the inner chamber being adapated to remain stationary in relation to the core and comprising a core catcher at one end and a wireline fishing neck at the other, the inner chamber also comprising a socket adapted for the reception of a wireline survey instrument and apertures above the socket for the passage of mud.

The survey instrument may be wirelined separately from the inner chamber or both may be runtogether.Alternatively,thecore barrel may be used in a conventional manner, ifwirelining is not desired.

In orderto accommodate the inner chamberfor wirelining purposes the traditional heavy drill collar with a small internal diameter,typically2 inches (5 cm),will need to have the internal diameter enlarged.

A latch mechanism is preferably provided to keep the inner chamber in position and a swivel to permit relative rotation between the outer and inner chaambers.

In order to provide for orientated coring, the core catcher may be fitted with scribing blades and the instrument socket may be orientated.

The preferred instrument is a wireline M.W.D.

(MeasurementWhile Drilling) instrument available from Exploration Logging Inc., a subsidiary of Baker International Inc. This uses mud pulse telemetry to send orientated survey information backto the surface while coring is taking place. Thus, it is unnecessary to stop drilling to take measurements with the resultthatcoring is quicker, operation is simplerandthere is less likelihood of jamming occurring than in magnetic multi-shop operations.

When an M.W.D. instrument is used the core barrel should be constructed from a non-magnetic material, e.g. Monel metal.

The invention is illustrated with reference to the accompanying drawing.

A core barrel comprises a rotatable outer chamber 1 and a stationary inner chamber 2. The outer chamber 1 is fitted with a conventional corehead 3 and the inner chamber 2with ascribed core catcher 4. The inner chamber 2 is closed near its top by means of a seal 5 into which is fitted an orientated latch 7 which locates and orientates a wireline M.W.D. tool 8 having a wireline fishing neck 9. The innerchamber2terminates in an annularwireline fishing neck 10.

Theflowpath of drilling mud is shown bythe direction of the arrows in the drawing.

The M.W.D. tool 8 and the inner chamber 2 can be pulled or run together or separately.

The core barrel is approximately 60 ft long (1 8.3m), 30ft (9.14m) to accomodate a core and 30ft (9.14m) to contain the wireline M.W.D. tool 8. The outer and inner chambers 1 and 2 are 7 and 31/4 inches in diameter respectively (19.7 cm and 8.3 cm respectively.

A latch mechanism 11 is provided to keep the inner chamber2 in position and a swivel 12to permit relative rotation between the outer and inner chambers 1 and 2.

Claims (7)

1. Acore barrel comprising an innerand an outer chamber, the outer chamber being rotatable and connectable at one end to a drill string and at the other end to a corehead, the inner chamber being adapated to remain stationary in relation to the core and comprising a core catcher at one end and a wireline fishing neck atthe other, the inner chamber also comprising a socket adapted for the reception of a wireline survey instrument and apertures above the socket for the passage of mud.

2. A core barrel according to claim 1 comprising a latch mechanism to keep the innerchamberin position.

3. A core barrel according to either ofthe preceding claims comprising a swivel to permit relative rotation between the outer and inner chambers.

4. A core barrel according to any of the preceding claims wherein the core catcher is fitted with scribing blades and the instrument socket is orientated.

5. A core barrel according to any of the preceding claims wherein the core barrel is constructed from a non-magnetic material.

6. A core barrel according to any ofthe preceding claims comprising in addition a wireline MWD instrument fitted into the socket.

7. Acore barrel as hereinbefore described with reference to the accompanying drawing.