GB2320735A - Cementing method for the juncture between primary and lateral wellbores - Google Patents

Abstract

A method for cementing the juncture between a primary 210 and a lateral 246 borehole comprises placing a parallel scoop head 254 in the primary borehole at a preselected position above the lateral wellbore, providing a liner 272 through the scoop head and into the lateral. Cement 274 is then pumped through the liner to pass through an aperture in the distal end of the liner and into an annulus defined between the liner and an earthen wall of the lateral borehole, until the cement has reached a level 276 within the primary wellbore which is above the juncture opening and below than the bottom surface of the parallel scoop head. The lateral wellbore may then be completed by known methods. A selective re-entry tool (300 fig.2J) may be used to maintain any function that could be done in a single wellbore, ie zonal isolation or stimulation.

Description

CEMENTING METHOD FOR MULTI-LATERAL COMPLETION AND THE JUNCTURE WITH LATERAL WELLBORES This document is divided from GB 2293186 which is directed to a method for cementing a multilateral wellbore having a primary wellbore and at least one lateral wellbore, using first and second plugs.

This invention relates generally to the completion of wellbores. More particularly, this invention relates to new and improved methods and devices for completion of a branch wellbore extending laterally from a primary well which may be vertical, substantially vertical, inclined or even horizontal.

This invention finds particular utility in the completion of multilateral wells, that is, downhole well environments where a plurality of discrete, spaced lateral wells extend from a common vertical wellbore.

Horizontal well drilling and production have been increasingly important to the oil industry in recent years. While horizontal wells have been known for many years, only relatively recently have such wells been determined to be a cost effective alternative (or at least companion) to conventional vertical well drilling. Although drilling a horizontal well costs substantially more than its vertical counterpart, a horizontal well frequently improves production by a factor of five, ten, or even twenty in naturally fractured reservoirs. Generally, projected productivity from a horizontal well must triple that of a vertical hole for horizontal drilling to be economical. This increased production minimizes the number of platforms, cutting investment and operational costs. Horizontal drilling makes reservoirs in urban areas, permafrost zones and deep offshore waters more accessible. Other applications for horizontal wells include periphery wells, thin reservoirs that would require too many vertical wells, and reservoirs with coning problems in which a horizontal well could be optimally distanced from the fluid contact.

Some horizontal wells contain additional wells extending laterally from the primary vertical wells.

These additional lateral wells are sometimes referred to as drainholes and vertical wells containing more than one lateral well are referred to as multilateral wells. Multilateral wells are becoming increasingly important, both from the standpoint of new drilling operations and from the increasingly important standpoint of reworking existing wellbores including remedial and stimulation work.

As a result of the foregoing increased dependence on and importance of horizontal wells, horizontal well completion, and particularly multilateral well completion have been important concerns and have provided (and continue to provide) a host of difficult problems to overcome. Lateral completion, particularly at the juncture between the vertical and lateral wellbore is extremely important in order to avoid collapse of the well in unconsolidated or weakly consolidated formations. Thus, open hole completions are limited to competent rock formations; and even then open hole completion is inadequate since there is no control or ability to re-access (or re-enter the lateral) or to isolate production zones within the well. Coupled with this need to complete lateral wells is the growing desire to maintain the size of the wellbore in the lateral well as close as possible to the size of the primary vertical wellbore for ease of drilling and completion.

Conventionally, horizontal wells have been completed using either slotted liner completion, external casing packers (ECP's) or cementing techniques. The primary purpose of inserting a slotted liner in a horizontal well is to guard against hole collapse. Additionally, a liner provides a convenience path to insert various tools such as coiled tubing in a horizontal well. Three types of liners have been used namely (1) perforated liners, where holes are drilled in the liner, (2) slotted liners, where slots of various width and depth are milled along the liner length, and (3) prepacked liners.

Slotted liners provide limited sand control through selection of hole sizes and slot width sizes.

However, these liners are susceptible to plugging. In unconsolidated formations, wire wrapped slotted liners have been used to control sand productions. Gravel packing may also be used for sand control in a horizontal well. The main disadvantage of a slotted liner is that effective well stimulation can be difficult because of the open annular space between the liner and the well. Similarly, selective production (e.g., zone isolation) is difficult.

Another option is a liner with partial isolations. External casing packers (ECPs) have been installed outside the slotted liner to divide a long horizontal well bore into several small sections.

This method provides limited zone isolation, which can be used for stimulation or production control along the well length. However, ECP's are also associated with certain drawbacks and deficiencies. For example, normal horizontal wells are not truly horizontal over their entire length, rather they have many bends and curves. In a hole with several bends it may be difficult to insert a liner with several external casing packers.

Finally, it is possible to cement and perforate medium and long radius wells are shown, for example, US Patent 4,436,165.

While sealing the juncture between a vertical and lateral well is of importance in both horizontal and multilateral wells, re-entry and zone isolation is of particular importance and post particularly difficult problems in multilateral well completions. Reentering lateral wells is necessary to perform completion work, additional drilling and/or remedial and stimulation work. Isolating a lateral well from other lateral branches is necessary to prevent migration of fluids and to comply with completion practices and regulations regarding the separate production of different production zones. Zonal isolation may also be needed if the borehole drifts in and out of the target reservoir because of insufficient geological knowledge or poor directional control; and because of pressure differentials in vertically displaced strata as will be discussed below.

When horizontal boreholes are drilled in naturally fractured reservoirs, zonal isolation is seen as desirable. Initial pressure in naturally fractured formations may vary from one fracture to the next, as may the hydrocarbon gravity and likelihood of coning. Allowing them to produce together permits crossflow between fractures and a single fracture with early water breakthrough jeopardizes the entire well's production.

As mentioned above, initially horizontal wells were completed with uncemented slotted liners unless the formation was strong enough for an open hole completion. Both methods make it difficult to determine producing zones and, if problems develop, practically impossible to selectively treat the right zone. Today, zone isolation is achieved using either external casing packers on slotted or perforated liners or by conventional cementing and perforating.

The problem of lateral wellbore (and particularly multilateral wellbore) completion has been recognised for many years as reflected in the patent literature.

For example, US Patent 4,807,704 discloses a system for completing multiple lateral wellbores using a dual packer and a deflective guide member. US Patent 2,797,893 discloses a method for completing lateral wells using a flexible liner and deflecting tool.

Patent 2,397,070 similarly describes lateral wellbore completion using flexible casing together with a closure shield for closing off the lateral. In Patent 2,858,107, a removable whipstock assembly provides a means for locating (e.g., re-entry) a lateral subsequent to completion thereof. Patent 3,330,349 discloses a mandrel for guiding and completing multiple horizontal wells. US Patent Nos. 4,396,075; 4,415,205; 4,444,276 and 4,573,541 all relate generally to methods and devices for multilateral completion using a template or tube guide head. Other patents of general interest in the field of horizontal well completion include US Patent Nos. 2,452,920 and 4,402,551.

Notwithstanding the above-described attempts at obtaining cost effective and workable lateral well completions, there continues to be a need for new and improved methods and devices for providing such completions, particularly sealing between the juncture of vertical and lateral wells, the ability to re-enter lateral wells (particularly in multilateral systems) and achieving zone isolation between respective lateral wells in a multilateral well system.

The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the several methods and devices of the present invention for completion of multilateral wells. In accordance with prior application serial no. 07/926,451 filed 7 August 1992, assigned to the assignee hereof, all of the contents of which are incorporated herein by reference, a plurality of methods and devices were provided for solving important and serious problems posed by lateral (and especially multilateral) completion including: 1. Methods and devices for sealing the junction between a vertical and lateral well.

2. Methods and devices for re-entering selected lateral wells to perform completion work, additional drilling, or remedial and stimulation work.

3. Methods and devices for isolating a lateral well from other lateral branches in a multilateral well so as to prevent migration of fluids and to comply with good completion practices and regulations regarding the separate production of different production zones.

In accordance with the present invention there is provided a method of cementing the juncture between a primary wellbore and a lateral wellbore comprising the steps of: a) placing a parallel scoop head within the primary wellbore at a preselected position above the lateral wellbore.

b) providing a liner through the scoop head and into the lateral; c) pumping cement through said liner and into an annulus defined by the liner and an earthen wall of the wellbore until the cement has reached a level within the primary wellbore which is above the juncture opening of the lateral and which is lower than a bottom surface of the parallel scoop head.

The above-discussed and other features and advantages of the present invention will be appreciated to those skilled in the art from the following detailed description and drawings.

Referring now to the drawings, wherein like elements are numbered alike in the several Figures: FIGURE 2A-J are sequential cross-sectional elevation views depicting a second preferred method for sealing a juncture between a vertical primary wellbore and lateral wellbores using cementation, perforation and permanent access equipment; FIGURE 2A is a cross-sectional elevation view depicting the cementing of a vertical wellbore; FIGURE 2B is a cross-sectional elevation view depicting liner cementation for a first lateral wellbore; FIGURE 2C is a cross-sectional elevation view depicting conventional ISO packer completion; FIGURE 2D is a cross-sectional elevation view depicting retrieval of the running tool; FIGURE 2E is a cross-sectional elevation view depicting the drilling of an upper (or second) lateral wellbore; FIGURE 2F is a cross-sectional elevation view depicting retrieval of the whipstock; FIGURE 2G is a cross-sectional elevation view depicting the installation of a diverter sub and parallel scoop head; FIGURE 2H is a cross-sectional elevation view depicting cementation of the upper (or second) lateral wellbore junction; FIGURE 21 is a cross-sectional elevation view depicting upper lateral (or second) wellbore completion; FIGURE 2J is a cross-sectional elevation view depicting the completion of the selective re-entry tool installation.

In accordance with the present invention, an embodiment of a method and device for completing lateral, branch or horizontal wells which extend from a single primary wellbore, and more particularly for completing multiple wells extending from a single generally for completing multiple wells extending from a single generally vertical wellbore (multilaterals) are described. It will be appreciated that although the terms primary, vertical, deviated, horizontal, branch and lateral are used herein for convenience, those skilled in the art will recognise that the devices and methods of the present invention may be employed with respect to wells which extend in directions other than generally vertical or horizontal. For example, the primary wellbore may be vertical, inclined or even horizontal. Therefore, in general, the substantially vertical well will sometimes be referred to as the primary well and the wellbores which extend laterally or generally laterally from the primary wellbore may be referred to as the branch wellbores.

This invention discloses a preferred method of cementing lateral wellbores extending from a parent or primary wellbore. This invention defines a method for the correct placement of the cement in lateral wellbores as well as the ability to control the cement as in a normal liner cementation job.

A preferred method especially useful for the purpose of zonal isolations is described below. This method maintains the ability to perform any function that could be done in a single well.

In Figure 2A a primary well 210 is drilled and the casing 212 is run in and cement 214 is installed in known manner. In Figure 2B a lateral wellbore #1, 216 is drilled off the bottom of primary wellbore 210 in a known manner. An appropriately sized liner 218 is cemented in place with cement 220, also in a known manner.

Referring now to Figure 2C, a work string 222, is equipped with a running tool 224. Below the running tool 224 is an appropriately sized PBR (polished bore receptacle) seal bore 226. Following the seal bore 226 is standard appropriately sized tubing 228 equipped with a multiplicity of appropriately sized ISO packers 230 and a multiplicity of sliding sleeves 232 ending in a standard bottom packer 234. The liner 218 and the liner cementation 220 has been previously perforated and completed by known standard completion methods.

In Figure 2D, the work string 222 (not shown) has retrieved the running tool 224 (not shown). Referring now to Figure 2E, a retrievable whipstock 240 along with whipstock orientation anchor 242 and whipstock packer 244 are run into primary wellbore 210 and fixed to casing 212 at the desired depth at which it is desired to drill lateral wellbore 22 designated as 246. Lateral wellbore 246 (lateral #2) is drilled with drill string 248 in a known manner.

As seen in Figure 2F, retrieving tool 250 withdraws retrievable whipstock 240 and whipstock orientation anchor 242 from primary wellbore 210.

Whipstock packer 244 becomes the reference point for the completion of lateral wellbore 246 (lateral wellbore #2).

Turning now to Figure 2G, a running tool 252 has the following equipment attached to it. A parallel scoop head 254, which contains a seal bore 256 which has a locating shoulder 258 that is capable of landing a liner (not shown). It should be noted that the aforementioned parallel scoop head 254 is located just above the juncture of lateral wellbore 246 (lateral #2) and primary wellbore 210. Below parallel scoop head 254 and above diverter sub 260 is a guide tube 262. At the bottom of diverter sub 260 is an orientation anchor 264. At the bottom of diverter sub 260 is an orientation anchor 264. Attached to the bottom of diverter sub 260 is a combination extension and locator seal assembly 26. The scoop head assembly 254, guide tube 262, diverter sub 260, locator seal assembly 266, together with their attachments and seals are run into primary wellbore 210 and set and seated with the aid of whipstock packer 244. At the completion of this operation, the seals are tested for leak-tightness and the final step as depicted in Figure 2G is to retrieve the running tool 252.

Referring now to Figure 2H, an appropriately sized liner 272 is run into the parallel scoop head 254 into lateral wellbore 246 (lateral #2) at the end of hydraulic release liner running tool 270. The juncture between parallel scoop head 254, and diverter sub 260 located in primary wellbore 210 and lateral wellbore 246 (later wellbore #2) are cemented with cement 274 using conventional known cementing methods.

It should be noted that parallel scoop head 254 should be in a vertical or substantially vertical section of the primary wellbore 210 so that the level 276 of cement 274 can be controlled to be below parallel scoop head 254 but at level 276, to completely seal the juncture between main wellbore 210 and lateral wellbore 246 and that level 276 be within the main wellbore 210.

In Figure 21, completion of lateral wellbore 246 (lateral wellbore #2) is done as follows: Firstly, a workstring 280 (not shown) is run into primary wellbore 210 which is equipped with known tools to perforate the liner 272 and the cement 274 of lateral wellbore 246, guided through the right hand bore 2828 of parallel scoop head 265 in a known manner. After the perforation operation is completed, workstring 280 is withdrawn from lateral wellbore 246 and primary wellbore 210. The lateral wellbore 246 is then completed by running an appropriately sized seal bore assembly 284 which has a multiplicity of ISO packers 286 and a multiplicity of standard sliding sleeves 288 ending in a standard bottom packer 290. The seal bore 284 is seated in the right hand bore 282 of the parallel scoop head 254.

The final step, as depicted in Figure 2J, for completion is to run a selective re-entry tool 300 whose left inverted Y" branch 302 is connected and seated into the left side seal bore 304 of parallel scoop head 354. The right inverted "Y" branch 306 is connected sealingly tight to the seal bore 384. This procedure maintains the ability to perform any function that could be done in a single wellbore such as zonal isolation, stimulation or any other desired function.

While an embodiment has ben shown and described, various modifications and substitutions may be made thereto without departing from the scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Claims (4)

CLAIMS:

1. A method of cementing the juncture between a primary wellbore and a lateral wellbore comprising the steps of: a) placing a parallel scoop head within the primary wellbore at a preselected position above the lateral wellbore.

b) providing a liner through the scoop head and into the lateral; c) pumping cement through said liner and into an annulus defined by the liner and an earthen wall of the wellbore until the cement has reached a level within the primary wellbore which is above the juncture opening of the lateral and which is lower than a bottom surface of the parallel scoop head.

2. A method of cementing the juncture between a primary wellbore and a lateral wellbore as claimed in claim 1 or claim 2 wherein the liner includes an axial aperture in a distal end thereof for passage of cement.

3. A method of cementing a multilateral wellbore as claimed in claim 1 wherein a further step comprises cementing the juncture between the primary wellbore and the lateral wellbore by pumping cement through said liner and into an annulus defined by the liner and an earthen wall of the wellbore until the cement has reached a level within the primary wellbore which is above the juncture opening of the lateral and lower than a bottom surface of the scoop head.

4. A method of cementing the juncture between a primary wellbore and a lateral wellbore substantially as hereinbefore described with reference to the accompanying drawings.