WO2011014055A1

WO2011014055A1 - A system for completing wells in unconsolidated subterranean zone

Info

Publication number: WO2011014055A1
Application number: PCT/MY2010/000128
Authority: WO
Inventors: Maharon Jadid; Mahmoud Abdel Rafea Wahba Mahmoud; Saradha Tirugnanasambandan; Mohd. Shahrul Amir Zamberi
Original assignee: Petroliam Nasional Berhad (Petronas)
Priority date: 2009-07-29
Filing date: 2010-07-21
Publication date: 2011-02-03

Abstract

A system (10) for completing gas wells in unconsolidated subterranean zone for preventing migration of sand with fluids produced therefrom is provided. The system (10) includes a well bore (15) completed with sand screen (20), at least one flow segmentation means (25) that prevents fluid flows from one segment (23) to another segment (23) along the sand screen (20), and a tubing (30) with elevated thickness at predefined position. Natural packing of the sand is thereby achieved along the sand screen (20) which acts as a gravel pack to the system (10).

Description

A SYSTEM FOR COMPLETING WELLS IN UNCONSOLIDATED SUBTERRANEAN

ZONE

FIELD OF INVENTION

The present invention generally relates to a system for completing wells in unconsolidated subterranean zone, and more particularly to an improved system for completing gas wells in unconsolidated subterranean zone to prevent migration of sand with fluids produced therefrom. BACKGROUND OF INVENTION

In the exploration and production of oil and gas, it is very common that sand production may be inevitable in fields that have a relatively low formation strength [< 68.9 x 10⁵ N/m² (<1000psi)]. In unconsolidated formations, loose sands and fines will migrate with hydrocarbon fluids produced by the wells. Detrimental effects of sand production are well-known by those involved in exploration and production of oil and gas, and these include the abrasion of pumping and other production equipment as well as reducing fluid production capabilities of the producing wells.

Selection of a suitable method for sand control needs to be viewed in terms of technical and economics point of view taking into account the elimination of sand production, maximizing productivity and well deliverability throughout the expected life of the well. In addition the above, the well completion, reservoir characteristics and sandface completion has to be taken into account before designing the sand control method.

There are various techniques to control sand production and one of the most popular option is sand screen with gravel pack system which have commonly been installed in the open hole well bores penetrating unconsolidated subterranean zones. In such system, the gravel pack serves as a filter surrounding the sand screen which helps to ensure that sand and other fine particles do not travel together with produced fluids into the well bores and through to the production tubing.

From a technical point of view from the industry experts developed over years, open hole gravel packing is an ideal method for sand control and well productivity as it minimizes the risk of screen plugging and subsequent erosion. But from the economics point of view, this is an expensive operation compared to Stand-Alone-Screen.

Open hole gravel packing is adopted in the completion scheme primarily on formation sand size distribution and its fines content indicates non-uniform sand formation. Based on Tiffin's criteria, for formation sand sizes D₅₀ < 75 μm and a large constituent of the formation is made up of fines (particles < 44 μm) whereby the uniformity co-efficient exceeds a value of 5 and sorting co-efficient exceeds a value of

10. These criteria direct the well completion design to gravel packing regardless of other parameters.

Commonly, in a sand screen with gravel pack system, a screen is positioned in the horizontal or vertical well bore which is to be completed whereby the screen is usually connected to several other production equipments which in turn connected to production string directly or via an elbow / joint for horizontal completion. Slurry of gravel particles which is usually known to those involved in the exploration and production of oil and gas as graded sand, is pumped down the production string and through the other production equipment downhole and then through the sand screen whereby the slurry of gravel particles are supposed to flow into the void spaces between the sand screen and the well bore, or also known as the annulus. Gravel particles from the slurry forms a gravel pack around the annulus surrounding the outside diameter of the sand screen while the fluids forming the slurry leaks off into the formation and/or through the sand screen. In such system, the sand screen as well as the gravel particles needs to be properly sized and/or selected to prevent sand and other fine particles from the formation to migrate with the produced hydrocarbon fluids into the well bore.

However, the sand screen with gravel pack for unconsolidated gas well completion suffers several shortcomings such as the gravel pack formed around the annulus using the typical methods mentioned above may be distributed non-uniformly and form sand bridges in the annulus. These sand bridges may further block the flow of the slurry of gravel particles through the annulus which in turn leave the void spaces in the annulus that are not covered by the gravel packs. As a result, when the well is placed on production, localized high velocity areas will be formed at said void spaces which subsequently cause the sand screen to be eroded and resulting in uncontrolled production of sand and fines.

There are several methods and apparatus that have been used to ensuring uniform distribution of gravel pack around the annulus, but those options as well as the gravel packing procedure itself are very costly, time consuming and involves relatively complex operations. Proper design for the selected screen and achieving natural packing mechanism around the selected screen and minimizing the high annular velocity around screen by considering flow segmentations, may replace Open Hole Gravel Pack in future operations.

Thus, it is believed that innovative system for completing unconsolidated wells, especially those that are gas-dominated with expected sand and fine contents production are needed so that completion could be done faster with less-complex procedure, and most importantly, at a cheaper cost. It is also important to note that such innovative system is able to limit the migration of formation sand with the produced fluids in a more economically attractive manner while allowing optimum production from the unconsolidated zones.

SUMMARY OF INVENTION

The present invention relates to a system for completing wells in unconsolidated subterranean zone for preventing migration of sand with fluids produced therefrom. The system generally includes a well bore completed with sand screen, wherein the sand screen is disposed from end portion of a heel section to a toe of the well bore; at least one flow segmentation means disposed at predetermined lengths along the sand screen, and a tubing with elevated thickness at predefined position. Accordingly, the heel section is defined as end section of a tubing which is tangentially extended at predetermined length from an elbow of the tubing in horizontal direction. The flow segmentation means prevents fluid flows from one segment to another segment along the sand screen, and natural packing of the sand is achieved along the sand screen which acts as a gravel pack to the system.

In the preferred embodiments, the well bore in the system is an open-hole well bore. Preferably, the sand screen is stand-alone sand screen and the flow segmentation means is an annular barrier. Accordingly, the segment is annular spacing between the flow segmentation means.

It will be appreciated that the tubing with elevated thickness is provided from vertical part of the elbow of tubing to end portion of the heel section. Accordingly, the tubing with elevated thickness connected at screen top covering the heel section.

BRIEF DESCRIPTION OF DRAWING

The accompanied drawing constitutes part of this specification and includes an exemplary or a preferred embodiment of the invention, which may be embodied in various forms. It should be understood, however, the disclosed preferred embodiments are merely exemplary of the invention. Therefore, the figure disclosed herein is not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention.

In the appended drawing:

FIG. 1 is a diagrammatic cross sectional side view of a system having a well bore completed with sand screen and flow segmentation means disposed therewith penetrating an unconsolidated subterranean zone, and tubing with elevated thickness is provided at predefined position of production string in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A detailed description of preferred embodiments of the invention is disclosed herein. It should be understood, however, the disclosed preferred embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention.

The preferred embodiments of present invention provide an improved system used for completing wells, especially for gas-dominated wells with expected sand and fine contents production in unconsolidated subterranean zones. Referring to FIG. 1 , the system (10) basically comprise a well bore (15) completed with sand screen (20), at least one flow segmentation means (25) disposed at predetermined lengths along the sand screen (20), and a tubing (30) with elevated thickness at predefined position of production string (35). It will be appreciated that the system (10) can be used for on- shore or offshore, highly deviated or horizontal wells. Accordingly, the preferred embodiments of the system (10) utilizes horizontal open-hole wells, but not limited to such use.

It will be appreciated that in most cases, highly deviated or horizontal open- hole wells are essentially used because of higher well productivities and lower completion cost. In the preferred embodiments, the system (10) utilizes a horizontal open-hole well that is completed with the sand screen (20) to control sand production and maximize the productivity. It is to be noted that the sand screen (20) used in the system (10) is a stand-alone sand screen.

In the preferred embodiments, the well bore (15) can be of, but not limited to conventional type known to those skilled in the art. The well bore (15) is completed with the sand screen (20) that continues disposed therewith from end portion (14a) of a heel section (14) to a toe (16) of the well bore (15). Accordingly, the heel section (14) is defined as end section of tubing (30) which is tangentially extended at predetermined length (L) from an elbow of the tubing (30) in horizontal direction. It will be appreciated that the sand screen (20) may be of various types, including but not limited to the commercially available screens such as wire-wrap, premium or expandable sand screen. It is to be noted that the system (10) is provided with flow segmentation means (25) disposed at predetermined lengths along the sand screen (20) to which a segment (23) is defined. Accordingly, the segment (23) is annular spacing between the flow segmentation means (25). The said flow segmentation means (25) are of substantially annular barrier disposed at predefined positions around the outer diameter of sand screen (20). It will be appreciated that the flow segmentation means (25) can be of, but not limited to flow constrictor of similar type as swell packers or any commercially available type of constrictors. The flow segmentation means (25) enable to segment the flow and to prevent fluid flows from one segment (23) to another segment (23) along the sand screen (20), thus preventing the formation of localized high velocity areas as well as reducing flow velocity and potential erosion of the sand screen (20).

By introducing the flow segmentation means (25) along the sand screen (20), the need of pumping slurry of gravel particles down to the production string (35) to form the gravel pack around the segment (23) of horizontal open hole well is eliminated. The flow segmentation means (25) enables natural packing of the sand achieved at each segment (23) along the sand screen (20). Said natural packing of the sand is achieved by particles or sands accumulated over period of time in production. Accordingly, the naturally packing of the sand will act similar to as gravel pack in the system (10) and maintaining the sand screen (20) ability to prevent the migration of sand or fine contents in underground reservoir (40) of subterranean zone into the production string (35). As a result, the preferred embodiments of the system (10) enable to eliminate shortcoming of producing and placing gravel pack which includes non-uniform distribution of gravel packs. The use of gravel-pack for sand-screen installation is expensive and its operation is highly complex and time-consuming. The flow segmentation means (25) enables to eliminate localized high velocity by preventing fluid flows from one segment (23) to another segment (23) along the sand screen (20) and therefore minimizing erosion of the sand screen (20).

It will be appreciated that the system further includes tubing (30) with elevated thickness at predefined position of production string (35). Accordingly, the tubing (30) can be of higher-grade or with thicken inner diameter at predetermined position of production string (35). It is to be noted that the tubing (30) with elevated thickness is preferably provided at predictable localized erosion area so that it provides additional safety precaution to the sand erosion. Accordingly, the tubing (30) with elevated thickness is provided from vertical part (30a) of the elbow of tubing (30) to end portion (14a) of the heel section (14). The tubing (30) with elevated thickness connected at screen top covering the heel section (14). It will be appreciated that the tubing (30) can be of various types, including but not limited to the commercially available type or custom made type. The production string (35) used for transporting fluids to a top surface or to a platform can be of any conventional type known to those skill in the art and will not be described herein.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation and various changes may be made without departing from the scope of the invention.

Claims

1. A system (10) for completing gas wells in unconsolidated subterranean zone for preventing migration of sand with fluids produced therefrom characterized in that the system (10) includes:- a) a well bore (15) completed with sand screen (20), wherein the sand screen (20) is disposed from end portion (14a) of a heel section (14) to a toe (16) of the well bore (15); b) at least one flow segmentation means (25) disposed at predetermined lengths along the sand screen (20); c) a tubing (30) with elevated thickness at predefined position; wherein the heel section (14) is defined as end section of a tubing (30) which is tangentially extended at predetermined length (L) from an elbow of the tubing (30) in horizontal direction; wherein the flow segmentation means (25) prevents fluid flows from one segment

(23) to another segment (23) along the sand screen (20); and wherein natural packing of the sand is achieved along the sand screen (20) which acts as a gravel pack to the system (10).

2. A system as claimed in claim 1, wherein the well bore (15) is an open-hole well.

3. A system as claimed in claim 1, wherein the sand screen (20) is stand-alone sand screen.

4. A system as claimed in claim 1 , wherein the flow segmentation means (25) is an annular barrier.

5. A system as claimed in claim 1 , wherein the segment (23) is annular spacing between the flow segmentation means (25).

6. A system as claimed in claim 1 , wherein the tubing (30) with elevated thickness is provided from vertical part (30a) of the elbow of tubing (30) to end portion (14a) of the heel section (14).

7. A system as claimed in claim 1 , wherein the tubing (30) with elevated thickness connected at screen top covering the heel section (14).