GROUTING WELL PLATFORM LEGS

Abstract: The annular spaced formed between a jacket leg (31) or a pile sleeve (32) and a pile (20) driven therethrough, or similar annular space of an offshore platform, has a particulate material and aqueous solutions of an alkali silicate material injected therein above a pile seal assembly (40). After flocculation of the silicate, the annular space is filled with grouting material.

Description: This invention relates to a method of grouting well platform legs, i.e. the annular space between either the jacket leg or pile sleeve and a pile driven therethrough, or any similar annular shape of an offshore platform used in well drilling and production. The prior art teaches several different methods of grouting the annular space formed between either a jacket leg or pile sleeve and a pile driven therethrough of offshore platforms. Typically, the methods involve setting a grout plug or column of grout which is supported either by the bottom of the body of water upon which the platform is installed or on a grout seal, and subsequently filling the annular space above the plug with grouting material. Such typical prior art grouting methods are illustrated in U.S. patents nos. Re 28,232; 3,468,132; 3,878,687; 4,009,581; 4,047,391; 4,052,861; 4,063,421; 4,063,427; 4,077,224; 4,140,426; 4,171,923; and 4,275,974. However, should such a grout plug or column not be supported by either a grout seal or bottom of the body of water, the grout will merely run out the bottom of the annular space into the surrounding water or area. Also, if some way of sealing the annulus cannot be found so that a grout plug or column can be placed in the annulus and allowed to harden, the annulus cannot be filled with grouting thereby affecting the stability of the offshore platform. Previously, when trying to seal the annular space a wide variety of materials have been used. Typically, fast setting gypsum cements have been tried, lost circulation materials used in well drilling have been tried, etc. In some instances where the annular space is accessible, divers have sealed or tried to seal the annular space by filling it from the bottom with sacks, rags, rubber materials, etc. However, the use of fast setting gypsum cements can plug up flow lines, and lost circulation materials used in well drilling operations have not proven satisfactory since they are usually not capable of bridging large open areas, and the use of divers is expensive. In wells, to consolidate the surface of a borehole in an incompetent formation and strengthen the bond between the surface of the borehole and cement placed therein, the prior art teaches the method of forcing a multivalent cation salt into the formation, thereafter forcing an alkali metal silicate solution which has a pH less than 12.0 containing at least 12% by weight silica into the formation, and thereafter forcing an aqueous cement slurry containing at least 2% by weight of a water soluble multivalent cation salt to contact the surface of the borehole. Such a prior art method is disclosed in U.S. patent no. 4,014,174. Another prior art method of grouting the annulus between either a jacket leg or pile sleeve and pile driven therethrough of an offshore platform, uses alkali silicate materials to initially seal the annulus to support a column of grout thereon so that the annular space may ultimately be filled with grouting material. Such a method is described in U.S. patent no. 4,493,592. Yet another prior art improved method of grouting the annulus between either a jacket leg or pile sleeve and a pile driven therethrough of an offshore platform, uses aqueous solutions of alkali silicate materials confined between a pair of pile seal assemblies in sealing the annular space formed between either a jacket leg or pile sleeve and a pile driven therethrough or similar annular sleeve space of an offshore platform to support a column of grout thereon so that the annular space may ultimately be filled with grouting material. Such an improved method and apparatus is described in our U.S. patent no. 4,552,486. We have now devised a grouting method which, whilst incorporating many of the features disclosed in our earlier U.S. patent no. 4,552,486, further improves on the grouting method described therein. According to the present invention, there is provided a method of grouting an annular space formed by an annular support member having a pile seal assembly thereon, the pile assembly comprising a pile seal member and a pile driven therethrough, of an offshore platform, said annular space being located between said annular support member and said pile and above said pile seal assembly, said method comprising the steps of injecting particulate material into said annular space to fill tears in the pile seal member and/or to bridge gaps between the pile seal member and pile; thereafter injecting an alkali silicate material which flocculates upon contact with a di- or multivalent cation fluid into said annular space; and after flocculation of said alkali silicate material, injecting cement or grout into said annular space to be supported by said seal assembly, said particulate material and the flocculated silicate therein. In order that the invention may be more fully understood, reference is made to the accompanying drawings, wherein: Fig. 1 shows an offshore platform having jacket legs and pile sleeves thereon having piling driven therethrough; and Fig. 2 shows a cross-section of part of a leg or pile sleeve with a pile driven therethrough. Referring to Fig. 1, an offshore platform 30 having a jacket portion 34, deck portion 33, jacket leg 31 and pile sleeve 32 is resting on the bottom of a body of water is shown having a seal assembly 40 installed on the bottom of each jacket leg 31 and pile sleeve 32. As shown, when installed, the platform 30 has the end of each jacket leg 31 and pile sleeve 32 embedded in the bottom of the body of water. Piles 20 are shown as being driven to depth through a jacket leg 31 and pile sleeve 32. Referring to Fig. 2, a seal assembly 40 which is used in the improved grouting method of the present invention is shown installed on an annular support member of the platform 30, such as a jacket leg 31, although it may be a pile sleeve 32, having a pile 20 driven therethrough. The grouting arrangement of most typically to be used by the present invention comprises a seal assembly 40 having a grout seal or pile wiper assembly therein, a grout system 60 having a control valve 64, surface grout line 62 leading to the control valve, a first line 66 leading from the control valve 64 to the annular space 70 formed between jacket leg and pile driven therethrough adjacent the grout seal or pile wiper assembly and a second line 68 leading from the control valve to the annular space 70 between the jacket leg and pile driven therethrough higher above the grout seal or pile wiper assembly. The seal assembly 40 comprises diaphragm assembly 41, pile seal assembly 42 and annular housing 45 connecting diaphragm assembly 41 and seal assembly 42. For the purposes of clarity herein, the term pile seal assembly 42 will refer to either a grout seal or pile wiper seal assembly, such as disclosed in the prior art described hereinbefore, or other such suitable means for enclosure of material. The diaphragm assembly 41 comprises an elastomeric diaphragm member which has been pierced by pile 20 being retained on the jacket leg 31 by means of annular flanges secured to housing 45. The pile seal assembly 42 comprises an annular elastomeric pile seal member 48 which sealingly engages the exterior of pile 20 being retained on the jacket leg 31 by means of annular flanges 50. While the diaphragm assembly 41 has been shown as connected to the pile seal assembly 42 by housing 45, the housing 45 may be eleminated and the diaphragm and pile seal member stacked between the annular flanges 50. The grouting system 60 on the jacket leg 31 comprises a surface grout line 62 running from the surface of the offshore platform to a location adjacent the lower end of the jacket leg 31 and a control valve 64 which communicates with annular space 70 formed between jacket leg 31 and pile 20 via lower line 66 and upper line 68. The control valve 64 may be of any suitable commercially available valve which is capable of alternately directing fluid flow between annular space 70 via lines 66 and 68 respectively; however, a ball actuated single sleeve sliding valve such as shown in United States Patent Number 4,275,974 is preferred. The improved grouting method of the present invention makes use of particulate material and other material that can be pumped into annular space 70 to seal the space, have great enough load bearing strength to support in conjunction with pile seal member 48 an initial grout column in annular space 70, and that will not plug the grout line 62 after pumping the material therethrough leaving the grout line 62 suitable for further use. The improved grouting method of the present invention which makes use of such particulate material and other material and comprises initially pumping or injecting a small fresh water spacer down the grout line 62 into the annular space 70, subsequently pumping or injecting particulate material down the grout line 62 into annular space 70, subsequently pumping or injecting an alkali silicate material which floculates upon contact with di- or multivalent cation fluids down the grout line 62 into the annular space 70 then actuating the valve 64 to prevent flow therefrom via line 66 while allowing flow therefrom via line 68 into annular space 70, next pumping or injecting a fresh water spacer of any desired amount into annular space 70 to clear any remaining alkali silicate material from line 62, control valve 64 and line 68 and subsequently pumping or injecting any suitable cement or grouting material down the grout line 62 into annular space 70 via line 68. If desired, a spacer fluid containing di- or multivalent cations, such as a potassium chloride solution, calcium chloride solution, etc., may be pumped into the annular space 70 before the initial fresh water spacer to provide a higher concentration of di- or multivalent cations in the annular spacer 70 with which the alkali silicate material may react. It should be understood that the amount of fresh water in the initial fresh water spacer should be small in comparison to the volume of annular space 70 so that the annular space 70 remains substantially filled with sea water or a di- or multivalent cationic fluid with which the alkali silicate material is to react. The function of the first fresh water spacer being to prevent floculation of the alkali silicate material with sea water contained in line 62, control valve 64 and line 66 before the entry of the alkali silicate material into annular space 70. Similarly, the function of the second fresh water spacer being to prevent floculation of the alkali silicate material remaining in line 62, control valve 64 and any which may have entered into line 68 while the material is being flushed from line 62, control valve 64 and line 68 to facilitate the injection of cement or grout into annular space 70. If desired, in addition to the initial amount of particulate material pumped into the annular space 70 to fill tears in the pile seal member 48 and/or bridge gaps between the pierced diaphragm and pile 20, additional sand, high strength synthetic fibers such a polypropylene fibers, cellulose flakes, ground walnut shells, and other types of lost circulation materials as well as various types of cement may be included or mixed with the alkali silicate material to increase its strength thereby increasing the amount of grout column the alkali silicate material will support in conjunction with pile seal member 48 in the annular space 70 during the grout injection portion of the improved grouting method. If the alkali silicate material in conjunction with the pile seal member 48 will not support a grout column in annular space 70 to completely fill the annular space 70 to the top of the jacket leg portion 34, after the initial grout in annular space 70 has hardened or set, a second injection of grout material into annular space 70 may be made to fill the annular space 70 from any convenient point on the jacket leg 31, such as from the top 35 thereof. Also, if desired, the top of the jacket leg 31 may be sealed and compressed air or gas may be injected into the annular space 70 between the jacket leg 31 and pile 20 extending therethrough to expell water from annular space 70 past pile seal 48 and the diaphragm of diaphragm assembly 41 into the sea floor so that the annular space 70 is substantially free of water before the injection of any material thereinto. However, if the water is expelled from annular space 70, unless the alkali silicate material is mixed with di- or multivalent cation fluid before the pumping thereof into the annular space 70 which mixing will increase the pumping pressure required to pump the material into annular space 70, it will be necessary to inject di- or multivalent cation fluid into the annular space 70 to floculate the alkali silicate material pumped thereinto. If desired, alternately, the particulate material and the alkali silicate material may be pumped into the annular space 70 and any residual sea water in the annular space 70 and any subsequent sea water leaking past pile seal member 48 and/or grout or cement in the annular space 70 may cause sufficient floculation of the alkali silicate material in annular space 70. The improved grouting method of the present can be used to seal the annulus between either a jacket leg or pile sleeve and a pile driven therethrough utilizing any type pile seal member 48 therein; or, any other annulus of an offshore platform where it is desired to support the pressure of a column of cement or grout. Since the particulate material and alkali silicate material taken in conjunction with the pile seal member 48 has load bearing capabilities sufficient to support a substantial column of grout in the annulus 70, in many instances, the improved grouting method and arrangement effectively eliminates the need for an inflatable type grout seal at the bottom of jacket leg 31 in many instances thereby allowing a less expensive grout seal or pile wiper to be substituted therefore. In those instances where the jacket leg 31 is not embedded in or resting on the floor of the body of water in which the platform is installed or the floor of the body of water is too soft or such a soft and muddy bottom to give effective bearing support, the pierced diaphragm, particulate material, and other material between the diaphragm and pile seal member 48 will help support the floculated alkali silicate material in annular space 70. The preferred particulate material to be injected into the annular space 70 to bridge any tears in the pile seal member 48 or bridge gaps between the pile seal member 48 and pile 20 prior to the injection of alkali silicate material into the annular space 70 is sand, although any readily available particulate material which may be easily pumped through the flow lines 62 and 66 and which has a specific gravity greater than sea water, such as sintered bauxite, shot, etc., may be used. The preferred alkali silicate material which floculates upon contact with di- or multivalent cation fluid or sea water to be used in the improved method of grouting of the current invention is an aqueous sodium silicate solution sold under the trademark FLO-CHEK® Chemical A additive by Halliburton Services, a division of Halliburton Company. An alternate material which can be used in the improved method of grouting of the present invention when mixed into an aqueous solution is a powdered silicate having a high ratio of silicon dioxide to alkali metal oxide sold under the trademark FLO-CHEK® P additive by Halliburton Services, a division of Halliburton Company. When using the preferred material, FLO-CHEK® Chemical A additive, in the improved method of grouting and arrangement of the present invention, any desired amount of material may be pumped or injected into the annulus to be grouted depending upon the strength required to support the desired column of cement or grout to be injected into the leg to form a plug or fill the annulus. Therefore, the length of the housing above the pile seal member 48 into which FLO-CHEK R Chemical A additive is pumped or injected into the annular space 70 to be filled should be preferably at least 1.2 m (four feet) in axial length of the annular space 70, to be sufficient to support an adequate column of cement or grout to be injected into the annular space 70 above pile seal member 48. Although FLO-CHEK R Chemical A additive or FLO-CHEK R P additive are the preferred materials to be used in the improved grouting method of the present invention, any alkali silicate having a molar ratio of silicon dioxide (SiO₂) to alkali metal oxide (sodium, potassium, ammonium or lithium) between approximately 1.6 or less to 4.0 may be used. Also, although it is preferred to use an initial spacer of fresh water before the injection of the alkali silicate material and spacer of fresh water after the injection of the alkali silicate material, the fresh water spacers may be eliminated, if the alkali silicate material can be prevented from flocculating during pumping through the grout line 62, grout control valve 64 and lines 66 or 68 before entering the annular space 70.

Claims: A method of grouting an annular space (70) formed by an annular support member (31) having a pile seal assembly (42) thereon, the pile assembly (42) comprising a pile seal member (48) and a pile (20) driven therethrough, of an offshore platform (30), said annular space (70) being located between said annular support member (31) and said pile (20) and above said pile seal assembly (42), said method comprising the steps of injecting particulate material into said annular space (70) to fill tears in the pile seal member (48) and/or to bridge gaps between the pile seal member (48) and pile (20); thereafter injecting an alkali silicate material which flocculates upon contact with a di- or multivalent cation fluid into said annular space (70); and after flocculation of said alkali silicate material, injecting cement or grout into said annular space (70) to be supported by said seal assembly (42), said particulate material and the flocculated silicate therein. A method according to claim 1, wherein the alkali silicate material is aqueous sodium silicate, aqueous potassium silicate, aqueous ammonium silicate or aqueous lithium silicate. A method according to claim 1 or 2, further comprising the steps of injecting a spacer of fresh water into said annular space (70) before the step of injecting the alkali silicate material thereinto; and injecting a spacer of fresh water into said annular space after the step of injecting the alkali silicate material into the annular space. A method according to claim 1,2 or 3, further comprising the step of injecting a spacer of di- or multivalent cation fluid into said annular space before the step of injecting an alkali silicate material thereinto. A method according to any of claims 1 to 4, wherein said annular support member comprises a jacket leg (31) of said offshore platform. A method according to any of claims 1 to 4, wherein said annular support member comprises a pile sleeve (32) of said offshore platform.

Inventors: KNOX, L. CARTER, MOORE, CLAYTON A.
Applicants: HALLIBURTON COMPANY
Application year: 1989
Main classification: E02B17
IPC codes: E02B17, E02D5, E21B33