Pre-filled drillpipe stands and method of preventing drilling mud loss

Abstract

The invention provides a method of preventing mud loss during a drilling operation using a drill string (20) assembled from a series of stands (22), of drill pipe sections, and a borehole assembly (BHA) with a drill bit (21) drilling in a well, the method comprising: a) provide pre-filled drill pipe stands (24) with a partly swelled water swellable fluid or gel (30), store said pre-filled drill pipe stands (24) in a drill pipe rack (42) of a drilling rig (40); monitor for mud loss while drilling, b) if detecting mud loss, then halt drilling, trip out a number of stands (22) to be replaced by a number of said pre-filled drill pipe stands (24), c) insert said number of one or more pre-filled drill pipe stands (24) in said drill string (20), d) circulate down said water swellable fluid or gel (30) from said pre-filled drill pipe stands (24) at least to beyond said drill bit (21 ), in order for said water swellable fluid or gel (30) to enter an assumed fracture causing said mud loss, e) pump until said water swellable gel (30) assumed to sufficiently fill fracture and swell to seal against mud loss, f) verify mud control, resume drilling.

Description

[0001] PRE-FILLED DRILLPIPE STANDS AND METHOD OF PREVENTING DRILLING MUD LOSS Introduction

[0002] The present invention relates to a method of preventing mud loss during a drilling operation using a drill string (20) assembled from a series of stands (22), each stand comprising two or three drill pipe sections, and a borehole assembly (BHA) with a drill bit (21) drilling in a well.

[0003] Background art

[0004] Mud loss in a well is highly undesirable. If the circulation of mud from a well is lost, less drilling mud is retrieved from the annular return channel in the well being drilled and the riser than is being pumped down through the drill pipe string. If the mud is lost to a permeable zone or fracture zone, the hydrostatic level of the return mud may sink to a level which no longer prevents lighter fluids to enter the well such as gas holding petroleum. Such gas may expand and create a kick which may bring the well out of control.

[0005] The applicant has a method of applying a partially swellable gel releasable from a downhole drill pipe borne annular tank during a drilling process, which is particularly useful for long and very long or deep wells, but requires such a downhole tank tool, and has the advantage of rapidly deploying the swellable gel near the drilling bit upon detection of loss of mud, which saves all the time required to pump swellable gel all the way down from the surface to the drilling bit and further to the leaking zone. However, a simpler method which does not require a downhole tank tool would be useful for shallow to medium wells.

[0006] A problem encountered in having a surface tank with swellable material is related to having to run the water swellable material from a deck tank through piping, mud pumps and valves ahead of entering the drill string. Water-holding fluid may be encountered and inadvertent swelling in pipes, pumps and valves ahead of entering the drill string, or in the drill string itself, creates a risk of partial or full blockage of passages from proper flowing of mud.

[0007] US 2023 / 0193706 Al describes atool that is used to inject a rapidly solidifying sealant into and across highly fractured oil and gas wellbore formations when a significant loss circulation zone or event is encountered. A system including the tool allows for application of the sealant to the formation without requiring removal of the drill string from the hole. The tool may have operative association with containers storing sealant and or sealant components that are provided downhole from the surface via wireline or the like.A problem encountered in having a surface tank with swellable material is related to having to run the water swellable material from a deck tank through piping, mud pumps and valves ahead of entering the drill string. Water-holding fluid may be encountered and inadvertent swelling in pipes, pumps and valves ahead of entering the drill string, or in the drill string itself, creates a risk of partial or full blockage of passages from proper flowing of mud.

[0008] N020230420 Al describes a method for preventing drilling mud loss during drilling, comprising: - providing a hydrophilic drilling mud loss treatment fluid, the hydrophilic drilling mud loss treatment fluid comprising: - water swellable hydrophilic polymer granules, - a first water tor partly swelling the first granule amount (Im), - a first hydrophobic oil inert opposite the water swelling polymer granules, - mixing the water swelling hydrophilic polymer granules and the first water and the first hy drophobic oil to partly swelled hydrophilic polymer granules (IP) with a hydrophobic oil film being formed between the partly swelled hydrophilic polymer granules (IP) for production of the hydrophilic drilling mud loss treatment fluid, - storing in a drilling pipe string borne tank behind a drill bit in a drill pipe string, - running the drill pipe string into a well, and drilling while monitoring of any undesired drilling mud loss during drilling, - upon detection of undesired drilling mud loss, opening a tank outlet and forcing out the drilling mud loss treatment fluid to a main bore in the drill pipe string, tire drilling mud loss treatment fluid, after the passage through the tank outlet, being mixed with a second water of drilling fluid in the main bore, and transported with the drilling fluid out through the drilling bit and penetrates into the mud loss zone surrounding the bore hole, where it continues to swell with the second water and formation water, and reduces or stops the undesired mud loss,

[0009] A problem which may be encountered using a downhole tank with swellable material to be released to the drill string and out through the nozzles is that swellable material may creates a risk of partial or full blockage of passages into or out of the tank and into the main bore or out through the drill bit nozzles and prevent proper delivery of water swellable material to the mud lozz zone intended.

[0010] Brief summary of the invention

[0011] The invention is defined by the independent claims 1 and 3. Embodiments are defined at least in claim 2.Brief figure captions

[0012] The invention is illustrated in the attached Figures, wherein

[0013] Fig. la illustrates a vertical section of a drilling operation in a well using a drilling rig with a riser and wellhead at the seafloor. The drilling operation may also be a land operation. Prefilled stands with swellable material is stored in the pipe rack. A loss of circulation is encountered during drilling and may interpreted as a mud loss to a permeable or fracture zone in the surrounding rocks.

[0014] Fig. lb illustrates an initial phase of the method of the invention, that the drilling is halted temporarily, one or more stands of drill pipe is tripped out and returned to the drill pipe rack when a mud loss to the surrounding rocks is inferred.

[0015] Fig. 1c illustrates a step of the invention, that we insert a corresponding number of pre-filled stands (24) with a partially swelled water swellable fluid or gel (30) from their storage in the drill pipe rack and included in an upper part of the drill string and ready to be pumped down by a trailing mud behind the sater swellable fluid or gel (30).

[0016] Fig. Id illustrates a next step of the invention that the water swellable fluid or gel (30) has been pushed out downwardly by the trailing mud called "upper mud", the water swellable fluid or gel (30) is on its way down through the drill string (20). Mud will ahead of the downward travelling water swelling fluid or gel (30) indicated as "lower mud (partly to loss) will most probably continue to be lost to the fracture formation.

[0017] Fig. le illustrates that the partially swelled fluid or gel (30) has passed out of the drill string and entered via the relevant portion of the well, here at the bottom of the so far drilled hole, and into a surrounding fracture zone or zone of permeable rock wherein the mud loss occurs. All the way from passing out of the drill bit and in the well and in the fractures, the partially swelled gel will encounter water from the drilling mud and the surrounding formation fluid and continue to swell until completely swollen, thereby progressively restricting passage of mud into the formation fractures and rock. Progressively one will regain mud control for intended circulation of mud to the surface.

[0018] Fig. If illustrates that drilling is resumed after mud control is regained.Fig. 2 illustrates a drillpipe rack (42) with pre-filled stands (24) of the invention arranged to the left, the stands (24) filled with partly swelled water swellable fluid or gel (30), and ordinary stands (22) which generally are the same as the pre-filled stands (24) when emptied.

[0019] Fig. 3 illustrates a lower and upper portion of one such pre-filled stand (24).

[0020] Embodiments of the invention

[0021] The invention provides a method of preventing mud loss during a drilling operation using a drill string (20) assembled from a series of stands (22), each stand comprising two or three drill pipe sections, and a borehole assembly (BHA) with a drill bit (21) drilling in a well, please see Fig. la.

[0022] The method comprises the steps of:

[0023] a) provide one or more pre-filled drillpipe stands (24), please see Fig. lb, with a partly swelled water swellable fluid or gel (30) and with removable end caps (26L, 26U), store said pre-filled stands (24), please see Fig. 3, in a drill pipe rack (42) of a drilling rig (40), please see Fig. 2; drill under circulation, and monitor for mud loss while drilling,

[0024] b) if detecting mud loss, the mud loss is assumed to enter a fracture in the rocks surrounding said well, and thereby reduced or no return mud circulation, see Fig. lb, then halt drilling, trip out a number of stands (22) to the rack, the tripped out stands (22) to be replaced by a number of said pre-filled stands (24),

[0025] c) insert said number of one or more pre-filled gel stands (24) in said drill string (20), Please see Fig. 1c,

[0026] d) pump drilling mud fortrailing behind the water swellable fluid or gel (30), circulate down their water swellable fluid or gel (30) from said pre-filled stands (24), please see Fig. Id, at least to beyond said drill bit (21), in order for said water swellable gel (30) eventually to enter said assumed fracture, the now emptied drill pipes of previously pre-filled stands (24) now functioning as ordinary drill pipe section stands (22). In an embodiment, reciprocate the drill string up and down to facilitate emplacement of said fluid or gel (30) out of the drill bit (21) and into the assumed fracture zone, e) pump until said water swellable gel (30) is assumed to arrive at and sufficiently fill an assumed fracture at a mud loss zone, please see Fig. le, and allow said swellable gel (30) to swell to seal against mud loss,f) verify mud control e.g. by measuring return flow to correspond to pumped down mud flow, and resume drilling.

[0027] The partly swelled swellable fluid or gel (30) may be of a hydrophilic polymer type, a crosslinked hydrophilic polymer which is delivered in bulk as a dry, generally water-free powder, which is partly swelled with a proportion of water, say 1 part powder partially swelled with 3 parts of water, and is filled into stands (22) to form pre-filled stands (24). Other pre-mixing proportions may be used depending on the swellable material used. The crosslinked hydrophilic polymer is superabsorbing. In an embodiment of the method the crosslinked hydrophilic polymer powder is used in one part which is potentially capable of absorbing about 60 parts of water, thus significantly expanding its volume. In an embodiment a gel forming substance may be added when mixing the 1 powder +3 water to form the partly swelled swellable gel (30) to be filled into the stands (24). The proportion for partially swelling may be varied. The 1+3 mixture is pumped into stands of e.g. 5" or 65 / 8" and sealed with end caps (26L, 26U). In an embodiment the fluid (30) is allowed to gelify sufficiently for being stored in the rack and handled on the drilling deck also after the lower end cap (26L) is removed. It is only a few seconds required from removing the lower cap (26L) before screwing the stand into the stand hanging in the spider in the drilling deck. The partly swelled swellable fluid or gel (30) is pushable using drilling mud or other circulation fluid, and may be circulated (pumped) down through the drill pipe string the ordinary way. The pre-filled stands (24) are advantageously prepared with its contents before transport to the drill pipe rack. When the partly swelled swellable gel (30) of an initial water content of 1 +3 is made subject to water available in the drilling mud and in the geological formation it may absorb the further 57 parts of water to finally swell to a 1 part hydrophilic polymer swollen with 60 parts of water eventually. The proportions given are not exact.

[0028] The invention also provides such pre-filled drill pipe stands (24) with a partly swelled water swellable gel (30) and with removable end caps (26L, 26U), arranged for being stored in a drill pipe rack (42) of a drilling rig (40).

[0029] The number of prefilled-stands (24) required to remedy one occurrence of mud loss or lost circulation, depends on the total volume of water swellable fluid or gel (30) in the number of pre-filled stands (24) required to eventually end up in the well. A 5" stand has a capacity of being filled with more than 500 liters of liquid.In an embodiment of the invention one may pump spacer ahead of and / or trailing the pill of partially water-swelled swellable fluid or gel introduced into the drill string, in order for the pill to encounter spacer fluid which not causes premature swelling of the pill fluid. However, tests have shown that the pill is pushed through the drill pipe without significant mixing with drilling mud, so spacer may not be required, particularly in shallow wells.

[0030] In an embodiment there may be some oil in the partly swelled water swellable fluid or gel (30).

[0031] A significant advantage of the invention is its simplicity: no further preparation needs to be done than providing stands (24) with partially swelled water swellable fluid or gel. When used, the emptied stands (24) are ordinary stands (22). Other methods using swellable or blocking material use swellable fluid material stored in external tanks which swellable material has to run through piping, pumps and valves.

[0032] Another significant advantage of the invention is that the partially swelled water swellable gel is inserted as a pill directly into the drill string. The "pill" itself does not have to run through pipes, mud pumps and valves ahead of entering the drill string. Thus, any inadvertent swelling in pumps and valves ahead of entering the drill string is avoided. In background art swellable material pumping into a well such material has to run through piping, pumps and valves from an external tank, a method which poses a risk of partial blockage by an often partially hardened swelling material which may block passages from proper flowing of mud.ref. component comment

[0033] numeral

[0034] 20 drill string a series of of two or more stands and provided with a drill bit (21) 21 Drill bit

[0035] 22 stand stand (22) of two or three drill pipe sections, usually tripped out one stand at a time from the well

[0036] 24 pre-filled stand stand (22, 42) pre-fdled with a partly swelled water swellable fluid or gel (30),

[0037] 26U, caps in top of 24, bottom of 24, protective cap at least in bottom of 26L respectively stand (24) to prevent loss of gel content. Ordinary protective transport caps may be used.

[0038] 30 partly swelled water swellable fluid or

[0039] gel (30),

[0040] 40 drilling rig, marine or land

[0041] 42 Drill pipe rack on drilling rig

[0042]

Claims

CLAIMS1. A method of preventing mud loss during a drilling operation using a drill string (20) assembled from a series of stands (22), each stand (22) comprising two or three drill pipe sections, and a borehole assembly (BHA) with a drill bit (21) drilling in a well, wherein the method is characterized by comprising:a) provide one or more pre-filled drill pipe stands (24) with a partly swelled water swellable fluid or gel (30) and with removable end caps (26L, 26U), store said pre- filled stands (24) in a drill pipe rack (42) of a drilling rig (40); monitor for mud loss while drilling,b) if detecting mud loss, then halt drilling, trip out a number of stands (22) to be replaced by a number of said pre-filled stands (24),c) insert said number of one or more pre-filled stands (24) in said drill string (20), d) circulate down said water swellable fluid or gel (30) from said pre-filled stands (24) at least to beyond said drill bit (21), in order for said water swellable fluid or gel (30) to enter an assumed fracture causing said mud loss,e) pump until said water swellable gel (30) assumed to sufficiently fill said fracture and swell to seal against mud loss,f) verify mud control, resume drilling.

2. The method of claim 1, further comprising a stepb2) after tripping out a number of stands (22), replace by the same number of said pre-filled stands (24).

3. Pre-filled drill pipe stands (24) characterized by being prefilled with a partly swelled water swellable fluid or gel (30) and with removable end caps (26L, 26U), arranged for being stored in a drill pipe rack (42) of a drilling rig (40).

Images