BRPI0502532B1 - Method and system for simulating pit wall breaker fluid in underground formation - Google Patents

Description

METHOD AND SYSTEM FOR SIMULATING FLUID WALL WALL TURNING BREAKER INSIDE TRAINING

UNDERGROUND

FIELD OF THE INVENTION The present invention relates to a method and system for simulating a plaster breaker fluid deposited on the wall of a well within an underground geological formation.

More specifically, the present invention relates to a method and system for simulating a breaker fluid deposited on the wall of a well within an underground geological formation, said plaster being deposited by the fluid (sludge) used. drilling the well and said well being an oil, gas water producing well or a well intended for the injection of fluids into an underground oil and gas producing formation. The method for simulating a plaster breaker fluid deposited on the wall of a well within an underground formation according to the invention comprises employing a system, such as the system of the invention, having a filter medium and a capacity applying pressure or dynamic conditions to form a plaster on the filter media from the initial use of drilling fluid (mud). The drilling fluid (sludge) is then replaced by the breaker fluid of the recoil, preferably without damaging the previously formed plaster with the drilling fluid (sludge). The plaster breaker fluid is then, in turn, subjected to the pressure and dynamic conditions of the inventive system, passing through the filter medium now already coated by the plaster. The amount of plaster breaker fluid passing through the filter medium is then monitored over time. An increase in flow or a drop in the pressure of plaster breaking fluid passing through the filter medium indicates the breaking of the plaster.

BACKGROUND OF THE INVENTION

Drilling fluid or drilling mud is used for drilling oil and gas wells for a variety of purposes including drilling drill lubrication, removal of debris from cut material from the wellbore and hydraulic stability of the drill. well. In order to achieve these objectives, a drilling fluid must have several characteristics, among which it is important to allow the formation of a layer or plaster deposited on the wellbore wall. The plaster serves to stabilize the well bore and prevent loss of the liquid portion of drilling fluid through the well wall toward adjacent geological formations. This loss of liquid from drilling mud, known as fluid loss, is a function of many variables involved such as drilling mud composition, type of formation encountered during the well drilling process, well temperature and pressure, etc. It is desirable to be able to test drilling mud under simulated well conditions in order to determine characteristics that the drilling mud should have in order to cope with previously simulated well conditions.

Although the presence of grout in the well wall is desirable during the drilling phase, grout removal is often desired after well drilling is completed, as the grout may interfere with the production of oil and gas from the well formation. . Thus, removal of the grout due to drilling fluids used to drill through formation oil and gas producing zones is particularly desirable.

Many highly permeable softer sandstone formations are completed with horizontal wells. They are usually open pit completions with screen or screen and gravel-pack. Plaster from drilling fluids or drill-in fluids, as well as the fluids used to drill through production zones, is conserved in the well until completion of completion operations. After completion, a cleaning solution is pumped into the well to remove plaster from the well. This cleaning solution may be, for example, an acid treatment or chelating agents, oxidants, enzymes or a combination thereof. The repeatability of plaster deposition becomes even more important when conducting sensitivity tests of the various components of a proposed cleaning solution. There is a need to automate plaster construction as well as testing the plaster breaker solution. Since the last decades there has been considerable increase in drilling of horizontal oil and gas wells, due to the improvement caused by the horizontal wells for both drainage and productivity of the producing reservoir. However, for operational and cost reasons, the completion of this type of horizontal well has been done in the open pit, using screen or gravel-pack. As a result of this increased demand for open well completion, specific drilling fluid systems have been developed for drilling the drilling zone of interest in horizontal wells, the so-called drill-in fluids. Thus, the drilling of the zone of interest in horizontal wells, in the vast majority of cases, has been done using drill-in fluid systems, which add simultaneous characteristics of drilling fluid and also of completion fluid, including They highlight: they are specific fluids for drilling producer reservoirs; fluid additives minimize damage to geological formation and thus maximize production; the fluid plaster provides effective control of the invaded zone during well drilling; They are biodegradable and low toxicity fluid systems.

In this way, drill-in fluid systems promote the formation of a well-formed plaster with good waterproofing and adhesion characteristics, which are desirable during the horizontal drilling phase, but nevertheless become problem when completing the open pit.

Thus, the effective disruption of plaster becomes increasingly essential to meet the current challenges of increasing oil and gas production.

Today, water-based drill-in fluid systems have been the most widely used. Its formulations are basically made up of xanthan gum (viscosifier), hydroxypropylated starch (filtrate controller), magnesium oxide (alkalizing), potassium chloride (KCI) or sodium chloride (NaCI) (for clay inhibition and as a thickening agent) and bridging agent, which may be micronized sodium chloride or sodium carbonate.

Some polymeric drill-in fluid systems form easily removable renders, requiring low drawdown, which is the pressure differential between reservoir and well. However, in most cases the lift off, or minimum pressure required for the breakage of the plaster, is greater than the drawdown of the production zone. In such cases, it is necessary either to optimize the composition of these fluid formulations to reduce lift off or the use of chemical removal methods such as the use of acids, oxidizers, enzymes, etc. ., among others. Opting for chemical removal involves a high additional cost due to the time of probe, the costs of additives, the labor involved, the logistics employed and the downtime of the well leading to loss of production or delayed entry into service. production, among other factors. For information, the average cost of an intervention in the Campos Basin is currently about $ 5 million ($ 5,000,000.00) per well.

Therefore, any reduction in lift off will result in significant savings by removing the plaster. And optimization in drill-in fluid formulations is one of the effective features that can be employed to minimize lift off. Lift off is related to the chemical composition of the fluid, the permeability of the production zone and the physicochemical characteristics of the fluid. And all these parameters can be related to the breaking pressure of the plaster. This would therefore be the pressure required to break the plaster adhered to the porous medium of the well wall in which the plaster formed.

From the foregoing, the technology currently available to address the problem of plaster disruption is either to use plaster-forming drill-in drilling fluids that can be removed at lower hydraulic pressures and thus more easily, or by use of drill-in plastering fluids whose breakage is achieved by chemical removal.

However, applications of plaster-producing drill-in fluids that can be removed by low hydraulic pressures are limited by the drawdown of the production zone between well and reservoir. In such cases, it is necessary to optimize the composition of these fluid formulations in order to reduce lift off, which is very costly to obtain on site and may involve considerable risks if not preceded by preliminary testing. preparatory measures that take into account all the variables involved. On the other hand, the use of chemical breakage solutions is limited by prohibitive costs resulting from the rental of the rig required for service, especially in the case of deep and underwater wells, and incurring additional costs with additives, labor -work and logistics employed, not to mention the downtime to which the well is relegated during the chemical cleaning processes used.

Current plaster breakage methods and systems either comprise directional applications directed to the use of specific equipment, or utilize intrinsic features to the details they address, or run into limitations of use dictated by the methods and systems hitherto used, such as see below.

Thus, US 6543276 teaches an oil well bore plaster rupture fluid testing method and equipment, which emphasizes the determination of the effectiveness and reaction time of the boulder rupture fluid deposited on the wall of a borehole. well penetrating an underground formation.

US 4748849, in turn, describes an apparatus for testing fluid loss characteristics of a test fluid such as drilling mud under static or dynamic conditions.

Other patents deal with methods for purely chemical removal of plaster.

Accordingly, US 6143698 and US 6131661 describe methods for removing grout from an underground well which comprises drilling the well using drilling fluid with grout-forming additives having an oxidation degradable component, preferably a polysaccharide or polymer, respectively. to facilitate future removal of the plaster. US 5783526 teaches a process for improving the removal of adhering solids from the inner surface of wells and sand control devices by contacting these solids with acidic solution. US 5501276 relates to a method and composition for removing dehydrated drilling fluid and well wall plaster by contacting the drilling fluid and plaster with an aqueous sugar solution that disintegrates them.

Also US 6631764 deals with grout removal and gravi pack methods for oil-based and water-based drilling fluids wherein the remaining grout may be ruptured by contact with grout breaking fluid containing at least one surfactant and a solvent.

Thus, as can be seen from the patenting of prior art patents succinctly described above, the existing methods and systems described therein do not meet the needs that the general problem of the rupture of plaster deposited on the wall of a well requires, or because they are. costly or limited to specific fluid conditions and types, or because they are based on absolutely impractical details and procedures under the conditions in which the problem unfolds, thus requiring the existing technique for a method and system which the present invention presents. .

As can easily be seen from the considerations outlined in this report, there are disadvantages to the present breakthrough technology deposited on the wall of a well that penetrates an underground geological formation, in particular the well being a horizontal well intended for exploration, prospecting. or production of mineral deposits, more specifically oil and gas deposits.

As stated earlier, existing technology is based on conventional methods and systems that either use laboratory tests with an emphasis only on the effectiveness and breakthrough time of the plaster, or that use purely chemical reaction treatments of specific characteristics, specially designed. for removal of certain types of plaster under certain conditions.

In addition, a disadvantage of the current art is that chemical treatment well cleaning solutions tend to be highly reactive and there is a risk that such solutions will remove grout at the circulation point before chemical treatment can be carried out. effect over the entire range of the open pit. This problem is especially common with cleaning solutions used to direct bridging particles used in production areas of interest, or with drill-in fluids. There is a demand for cleaning solutions that have an effect This delay allows the cleaning solution to circulate through the gap before leakoff, or before flow occurs from any portion of the formation from which the plaster has been removed. If the cleaning solution or plaster breaker solution is in place within the borehole, the solution begins to react with the plaster to remove it.If the delay could be long enough, the breaker solution could be “severi pack.” The disruption time for such an application would need to be within a range of approximately four to twenty-four hours, depending on whether or not to control fluid loss during subsequent piping trips.

Thus, another technical disadvantage of the state-of-the-art systems and methods currently employed is that plaster breakage tests for this type of delay could be extremely time consuming and prone to test-to-test variations if performed manually.

An additional disadvantage of the current technique is that because of the great depths of the sea where oil and gas are increasingly being prospected and produced nowadays, the chemicals applied in the treatments for removal of the plaster become liable to change. yield and behavior caused by the long distances at low temperatures of the regions that these substances need to travel on the round trip between the surface platform on which the substances are prepared and the well at the bottom of the sea.

In addition, a disadvantage associated with the above would be the large volumes of required chemicals employed, in proportion to the large depths in which the wells are located, requiring higher capacity systems and equipment for the preparation of said chemicals, therefore more expensive and involving immobilization of the wells. higher costs.

From an environmental point of view, the longer the path to which chemicals for grout removal are required to travel, the greater the potential risk of leakage and damage to the environment. In addition to the technical difficulties mentioned above, there are those of an economic nature as state of the art systems and methods currently employed for the use of chemical treatment well cleaning solutions, when requiring the use of well service probes, involve cost additional high due to the rent of the rig, additives, labor and logistics employed.

An additional economic disadvantage is that it results from the downtime to which the well is subjected during the chemical cleaning processes used, with lost profits resulting from the loss of production or the delay in the well coming into production, among other factors.

Even as an economic disadvantage that the downtime of the well for chemical removal of the plaster causes, there are the reflexes in ongoing projects that depend on the production of the paralyzed well, such as non-compliance and subsequent expansion of the various phases of the project and the deadline. consequent postponement of expected financial returns, thus affecting the cash flows of these projects. Any fines for failure to meet production targets previously committed to government regulatory agencies, contractors, business partners, investors, etc. will reflect the entire operational chain of users' project portfolios with damaging consequences for financial planning and budget control and of costs of the projects involved.

Likewise, the fact that the current technique of chemical removal of plaster requires equipment specifically designed and built for service in deepwater submersible wells, makes equipment of scarce availability in the market of equipment to work in these conditions, leading to long times. waiting for the opportunity to use these equipments that are often coming from other regions of the globe. This fact, in addition to frequently generating high transportation and insurance costs as well as premium price in advance to enable and pre-reserve equipment access by users, causes other disadvantages in ongoing projects that depend on the use of such equipment. , such as non-compliance and subsequent lengthening of terms.

Thus, despite existing developments, the technique still requires cheaper, faster and more readily available methods and systems for disrupting the plaster deposited on the wall of a well located within an underground geological formation, the deposited plaster being said. by the fluid (mud) used in drilling the well and said well being an oil, gas, water producing well or a well intended for the injection of fluids into an underground oil and gas producing formation, such methods and systems being described and claimed in this application.

SUMMARY OF THE INVENTION

In a simplified manner, the method of simulating a plaster breaker fluid deposited in the wall of a well within an underground geological formation according to the invention comprises applying pressure or dynamic conditions to a drilling drilling fluid (sludge). in order to form a plaster in a filter medium, and then to replace the drilling fluid (mud) with a plaster breaking fluid, preferably without damaging the previously formed plaster with the drilling fluid (mud). Said method also further comprises applying pressure or dynamic conditions to a plaster breaking fluid. The amount and pressure of plaster breaking fluid passing through the filter medium is then monitored over time and an increase in the flow or drop in pressure of plaster breaking fluid passing through the filter medium indicates the rupture of the plaster. simplified, the system for simulating a plaster breaker fluid deposited on the wall of a well within an underground geological formation according to the invention is a system for applying the method of the invention and comprises the use of a forming unit plastering and plaster breaking unit. The method and system of the invention thus permits numerous simulations for plaster breaker fluid from the use of different filter plug compositions, each corresponding to the material of each perforated geological formation found underground, and from the use of each type. drilling fluid (mud) used in drilling wells, enabling you to identify in advance which plaster remover or breaker would be the most suitable to be used for each drilling geological material and for each type of drilling fluid (mud) used, as well as under which dynamic conditions each type of breaker fluid should be applied in order to minimize the risk of damage to geological formation and maximize well production. The invention thus provides a method for simulating a breaker fluid deposited on the wall of a well located within an underground geological formation, whatever the fluid (mud) used for drilling the well and whatever the material of the formation. underground geology using conventional equipment.

The invention further provides a system consisting of plaster forming unit and plaster breaking unit, such system allowing the proposed method to be realized. BRIEF DESCRIPTION OF THE DRAWINGS The attached FIGURE 1 illustrates a schematic view of the flowchart of the filtration unit, the filtering unit. plastering of the system of the invention. The accompanying FIGURE 2 illustrates a schematic view of a diagram of forces acting on the plaster forming unit and plaster breaking unit of the system of the invention. The accompanying FIGURE 3 illustrates a schematic cross-sectional view of a diagram of the forces acting on the plaster and the breaking mode of the plaster as the polymer content in the plaster varies. The accompanying FIGURE 4 illustrates a schematic cross-sectional view of a diagram of the forces acting on the plaster and the breaking mode of the plaster as the inert solids content of the plaster varies. The accompanying FIGURE 5 illustrates a diagram of the variation of plaster burst pressure with xanthan gum concentration. The accompanying FIGURE 6 illustrates a diagram of the variation of plaster breaking pressure with HP starch concentration. The accompanying FIGURE 7 illustrates a diagram of the variation of plaster burst pressure with fluid lubricant concentration. The accompanying FIGURE 8 illustrates a diagram of the particle size distribution of fine calcium carbonate versus percent passing mass. The accompanying FIGURE 9 illustrates a diagram of the particle size distribution of the average calcium carbonate versus the percent passing mass. The accompanying FIGURE 10 illustrates a diagram of the variation of plaster burst pressure with the type of bridging agent. The accompanying FIGURE 11 illustrates a diagram of the effect of bridging agent concentration on plaster burst pressure. The accompanying FIGURE 12 illustrates and a diagram of the effect of the concentration of perforated solids on the burst pressure of the THIXCARB plaster. The accompanying FIGURE 13 illustrates a diagram of the effect of the influence of permeability on the breaking pressure of the plaster. The accompanying FIGURE 14 illustrates a diagram of the effect of the breaker fluid pH influence on the burst pressure of the THIXCARB plaster.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used in the invention, "plaster" is the material deposited on the wall of a well drilled in underground geological formation, said material coming from particles suspended in the fluid (mud) used in the drilling of said well, which agglutinate under the action of pressure and temperature inside the well. “HTHP Cell” is equipment designed to provide high temperature and high pressure conditions to an existing material inside. The term “drill-in” refers to a type of fluid that aggregates both drilling fluid and completion fluid characteristics and is used to drill through oil or gas producing zones. The term "breaker fluid" means any material having a gaseous, liquid or solid flow capacity, alone or in admixture in any proportion, capable of displacing the plaster deposited by the fluid (mud) employed in drilling a well wall underground. Thus the disrupting fluid may be in liquid, gaseous or solid state or in admixture of any proportion of these physical states.

Formation is the potentially producing underground geological formation, for example, an oil and gas producing formation.

Reservoir is the rock of the production formation located in the ground or underground that contains a mineral reserve, deposit or accumulation, for example hydrocarbon, oil and / or gas reservoir.

As can easily be seen from the considerations outlined in this report, the disadvantages for current underground wall-mounted plaster disruption technology, such as major costs and risks arising from obtaining “on-site” fluid formulations used or The multiplicity of equipment employed, as well as environmental aggression, when opting for the chemical treatment of plaster, are greatly reduced or even eliminated in the method and system proposed in the present invention.

Thus, in a preferred embodiment of the invention, the method comprises utilizing a plastering unit and applying pressure to a hydraulic fluid such that said pressure fluid displaces a piston against a drilling fluid (mud) filled chamber, the said drilling fluid (sludge) being forced against a filter medium composed of a porous plug to form at the opposite end of the plug a layer composed of particles suspended in the drilling fluid (sludge) which solidify therein after a certain time, thus constituting a plaster. Thereafter, the drilling fluid (mud) is replaced with a solution of plaster removal or breaker fluid, preferably without damaging the plaster previously formed with the drilling fluid (mud). The plaster breaker fluid is then in turn subjected to pressure and forced to pass through the filter media now coated by the plaster. The pressure and amount of plaster breaker fluid passing through the filter medium are then monitored over time. An increase in flow or a reduction in plaster breaking fluid pressure passing through the filter media recorded on the flowmeter or pressure gauge indicates the rupture of the plaster.

Still according to a preferred embodiment of the invention, the system of the invention is a system which allows the application of the method of the invention and comprises plaster forming unit and plaster breaking unit.

According to another preferred embodiment of the invention, the plaster forming unit is an HTHP cell.

According to another preferred embodiment of the invention, the filtering medium of the plaster forming unit is a plug formed of porous rock such as sandstone.

Also according to a preferred embodiment, the system of the invention comprises a hand-operated air pump, hydraulic fluid transfer system, hydraulic fluid reservoir, hydraulic piston, mineral oil compression chamber, filter plug, plug protection membrane, storage of plug, main cylinder, pressure gauge and plaster.

Alternatively, the plaster forming unit and the plaster breaking unit are laboratory test units.

Alternatively also, the plaster forming unit and the plaster breaking unit are the same unit.

Alternatively, the manual air pump is a hydraulic pump.

Alternatively, the manual air pump is an automatic pump.

Alternatively, the well within the underground geological formation is a well producing oil, gas, water separately or in admixture.

Alternatively, the well within the underground geological formation is a well for the injection of fluids into an underground oil and gas producing formation.

Alternatively also, the well within the underground geological formation is a horizontal well.

Alternatively, the well located within the underground geological formation is a well that is completed by an open well with screen or gravel-pack.

Alternatively, the drilling fluid used in the well is a drill-in fluid.

Alternatively, the drilling fluid (mud) used is kept in the well until completion of the completion operations. The present invention will be described below with reference to the accompanying Figures. The accompanying FIGURE 1 illustrates a schematic flow chart view of the plaster forming unit of the inventive system consisting of an HTHP filter cell using plugs as the filter medium. Grouting is done in the HTHP filter cell where the filter medium is a sandstone plug or other porous rock. Prior to HTHP filtration testing, the plugs are saturated with synthetically formed water, 30,000 ppm brine (NaCl) brine. Table 1 below contains information about the plugs used. For each batch of tests plugs with permeability similar to that of Berea sandstone were used. TABLE 1 Table 2 below shows the composition of the synthetic forming water. TABLE 2 This HTHP filtration has the duration of time required to achieve stability in the plaster thickness, being performed at 80 ° C and with a pressure differential of 500 psi. Table 3 below compiles operating parameters used in the HTHP filtration and plaster burst tests. TABLE 3 After filtration, the plaster plug is transported as quickly as possible to the plaster breaking unit to prevent said plaster from undergoing a dehydration process from the moment it is removed from the HTHP filter cell. , thus becoming gradually more dehydrated over time. The plastered plug is then jacketed into the Viton membrane and positioned in the plaster breaking unit. The oil used for breaking the plaster is mineral oil, as it is easy to handle and purchase, and dead oil can also be used. The plaster breakage test comprises pressurizing the plaster coated plug via chambers of the plaster breakage unit and manual hydraulic pump. As the plaster is pressurized, the pressure gauge of the plaster breaking unit will indicate the value of the normally increasing pressure acting on the plaster. As soon as the oil breaks the plaster, the pressure gauge will decline. The maximum pressure value reached before the pressure decline is called plaster burst pressure.

As illustrated in the accompanying FIGURE 2, the hand-operated pneumatic pump (1) provides pressure for the breaking of the plaster, said pressure being transmitted through a hydraulic fluid that passes through line (2) and is stored in the reservoir (3). The hydraulic fluid under pressure drives the piston (4) which transmits the pressure it receives to the mineral oil contained inside the chamber (5). In turn, the mineral oil is pressed against the plug (7) consisting of a porous medium that acts as a filter medium, until said mineral oil reaches the pressure necessary and sufficient to break the plaster (10) formed at one end. plug (7). Viton membrane (6) is used to wrap and protect the plug (7) and also to direct the flow of hydraulic oil contained in the chamber (5) against the plaster (10). The cylinder (8) storing the Viton membrane-jacketed plug (7) is connected at its lower end to the fluid storage main cylinder (11), which contains both reservoir hydraulic fluid (3) and chamber mineral oil (5) as well as the piston (4). The main fluid storage cylinder (11) is connected at its lower end to the hand air pump (1) and at its upper end to the pressure gauge (9).

Otherwise, plaster breakage tests made several observations possible.

Thus, in rupture tests where the plaster undergoes variations in polymer concentrations (xanthan gum and HP starch) and the lubricant LIOVAC 4260, there was a tendency of rupture of point-type plaster, as is usually the case in wells horizontal. That is, there is no disruption of significant portions of the plaster but small portions of the plaster as illustrated by FIGURE 3.

Another aspect is that the plaster formed in a porous medium is initially created internally in that medium, and then grows externally to that porous medium. Thus, the foundation of the plaster is located on the inside of the porous medium. Consequently, the deeper the inner plaster, the more stable the plaster will be, as it will be more firmly adhered to the porous medium.

On the other hand, the strength of the external plaster depends on the depth of the internal plaster and also on the cohesion of the material that composes the plaster. Thus, the higher the concentration of cementitious material (polymer mass, lubricants, etc. found in the plaster) and the depth of the internal plaster, the more difficult is the rupture of the plaster.

However, as the content of cementitious material decreases and the content of inert solids in the plaster increases (such as calcium carbonate, perforated solids, etc.), the breakage of the plaster becomes easier.

Breaking tests also showed some trends in plaster formation. For example, in tests where the concentration of polymers and fluid lubricant varied, a tendency was observed to form thick inner or thick inner plaster or thin outer plaster. led to an increase in the difficulty of breaking the plaster. It was also observed that the plaster mass had a predominance of cementing material in relation to the inert solids content. Due to all these factors, the point of rupture of the plaster predominated, with the release of small portions of the plaster, as shown in FIGURE 3. In the tests with variation in the inert solids content, the formation of another type of plaster characterized by the presence of Thick external plaster combined with a shallow, virtually non-existent inner plaster. The mass of these renders contained proportionally high inert solids content. Due to these factors, generally easy to break renders were obtained which ruptured in large portions as illustrated by FIGURE 4.

With respect to the breaking pressure of the plaster, the tests made it possible to establish relationships between this breaking pressure and some variables such as xanthan gum concentration, starch HP concentration and fluid lubricant concentration.

Thus, the graph of FIGURE 5 illustrates the effect of xanthan gum concentration on the breaking pressure of the plaster, starting from four different concentrations in THIXCARB fluid samples, namely: 1.0; 1,2; 1.5 and 2.0 Ib / bbl (pounds per barrel). From the graph it can be seen that the pressure required for the rupture of the plaster grew a lot with the increase of xanthan gum concentration in the breaker fluid. From the results of the tests, it is observed that the optimal concentration of xanthan gum in THIXCARB fluid would be between 1.0 and 1.5 Ib / bbl, above this range the required burst pressure greatly increasing. The graph in FIGURE 6 shows the results of variations in the concentration of filtrate reducer (HP starch) in the THIXCARB formulation over the breaking pressure of the plaster. Analogous to xanthan gum trials, there is also a tendency for the grouting burst pressure to increase with increasing starch HP concentration. However, the breakthrough pressure / starch HP concentration ratio was slightly lower than the breakthrough pressure / xanthan gum concentration ratio, especially at higher concentrations. Still from FIGURE 7, it is noted that the ideal concentration for HP starch would be around 1.4 Ib / bbl, thus ensuring a low level of plaster breakage. However, such concentration does not meet the filtrate control needs used in operating activities, and it is the fluid specialist's responsibility to consider the use of HP starch in order to simultaneously meet operational needs and minimize plaster burst pressure.

Referring to FIGURE 7, the graph illustrates the growth tendency of plaster breaking pressure with increasing concentration of LIOVAC 4260 lubricant in the THIXCARB formulation, thus suggesting that said lubricant be used at low concentrations. Still in FIGURE 8, it is noticed that concentrations above 1% (one percent) by volume cause marked increases in the breaking pressure of the plaster, even at a higher rate than in the case of xanthan gum concentration.

In order to identify the influence of bridging type on plaster breaking pressure, four different THIXCARB breaker fluids were produced with the same composition but containing different bridging agents. Thus, in the first fluid a fine calcium carbonate at a concentration of 35.0 Ib / bbl was used (see particle size distribution curve of FIGURE 8), in the second fluid an average calcium carbonate at a concentration of 35.0 Ib / bbl ( see particle size distribution curve of FIGURE 9), a third mixture of glass microsphere at a concentration of 10.0 Ib / bbl and a medium calcium carbonate at a concentration of 20.0 Ib / bbl was used in the third fluid and a fourth fluid was used. baritin at 35.0 Ib / bbl. For each of these fluids a plaster breakage test was performed using Berea sandstone plugs with close permeability, the results of the tests being shown in FIGURE 10. The tests indicated that the lowest plaster breakage pressure was presented by the plug. of fine calcium carbonate, followed by increasing order of breaking pressure of plaster the glass microsphere plug with medium calcium carbonate, showing the baritine and medium calcium carbonate plugs much higher pressure values breaking plaster.

Currently used TH IXCARB formulations typically use medium calcium carbonate. Thus, from the results expressed in FIGURE 10, it is suggested to use thin calcium carbonate or, when it is not possible to make use of said carbonate, to use the mixture of medium and thin calcium carbonate, in a larger proportion of as thin as possible to reduce plaster burst pressure.

Still aiming to identify the influence of the type of bridging on the rupture pressure of the plaster, other tests were made with plasters generated from formulations with four different concentrations of medium calcium carbonate, as follows: 10 .0; 20.0; 30.0 and 40.0 Ib / bbl. FIGURE 11 shows the result of these tests, showing that the breaking pressure of the plaster drops significantly with increasing calcium carbonate concentration. Thus, the use of concentrations above 30.0 Ib / bbl is desirable for low plastering burst pressures.

A major concern during drilling wells is the control of the residual solids content in the grout generating drilling fluid, as these residual solids cause several undesirable consequences such as increased consumption of drilling fluid additives, wear of pump pumps. mud and drill, among others. In addition there is also the question of the influence of the concentration of said solids on the breaking pressure of the plaster, whose response was given by the breaking tests with TH IXCARB formulated plasters at different concentrations of perforated solids (gravel). The cuttings used in these trials had 40% (forty percent) of crushed Berea sandstone and 60% (sixty percent) of ground Calumbi shale. In addition, Berea plugs of the same magnitude of permeability were used. FIGURE 12 illustrates the results of the aforementioned THIXCARB renders disruption tests in which the concentration of perforated solids was varied to the concentration tested, with concentrations less than or equal to 5% (five percent) by volume being The breaking pressure of the plaster showed a downward trend with increasing concentration. However, at high concentrations, ie, greater than or equal to 10% (ten percent) by volume, an upward trend in plaster bursting pressure was observed.

In order to evaluate the influence of porous media permeability on the rupture pressure of the plaster, renders of the same THIXCARB fluid sample were tested on Berea plugs with the permeability of 100, 700 and 1025 mD (milidarcy).

The results evidenced a tendency of reduction of the rupture pressure of the plaster with the increase of the permeability, as FIGURE 13 illustrates. This fact suggests that formulation optimizations, with a view to reducing plaster breaking pressure, are more necessary for low and medium permeability than for high permeability. FIGURE 14 shows the behavior of THIXCARB renders burst pressure when varying the pH of the renders generating fluid. Grouts from the same THIXCARB fluid sample were generated and plugs with close permeabilities were used. The results suggest that the burst pressure increases with increasing pH and apparently lower lift off pressure is required for acidic or intermediate pH THIXCARB fluids. However, when the pH approaches the most alkaline range of high pH values, a larger increase in the pressure required for the breakage of the plaster is observed, suggesting that THIXCARB formulations work with pH of intermediate values. Table 4 below describes the composition of the plaster breaking fluid formulation used in the plaster breaking tests. TABLE 4 On the other hand Table 5 below compiles the functionality of the main additives used in the THIXCARB system. Within the context described above, what the method and system of the invention proposes is the use of a new approach to testing of plaster breakage simulators based on new concepts involving the optimization of the conditions in which plaster breakage is obtained.

Thus, a technical advantage provided by the method and system of the invention is that it does not require "on-site" optimization optimization in the composition of reduced "off-off" plaster breaker formulations.

This technical advantage of the invention translates into practical economic advantage in terms of time, cost and risk, as it enables preliminary laboratory preparatory tests to be performed which take into account all the variables involved in the formulation of the appropriate plaster breaker fluid.

Thus, according to the concept of the invention, another economical advantage that the invention provides is the cost savings achieved by eliminating the need for the use of chemical treatment well cleaning solutions, thus also avoiding high additional rental costs. of well service rigs with additives, labor and logistics employed.

It should also be noted that the use of the method and system of the invention in wells located in deep water depths, while eliminating the need for the use of chemical well cleaning solutions, also makes it possible to dispense with the current technique which requires equipment specifically designed and constructed. for service in deepwater submersible wells, of low availability in the market, associated with long waiting times for the opportunity to use these equipments that are often coming from other regions of the globe. Finally, it also allows savings with frequently high transportation and insurance costs as well as premium price prepayment for enabling and pre-booking access to such equipment by users, with disadvantageous consequences on ongoing projects, such as non-compliance and subsequent lengthening of terms.

A further additional economic advantage that the invention provides is that, by eliminating the need for the use of previously treated chemical treatment well cleaning solutions, the well is no longer subject to prolonged periods of inactivity as a result of probe operation. This way, the production losses resulting from the interruption of well production are definitively removed, thus resulting in higher productivity, as well as possible anticipation of the production of new wells, resulting in anticipation of revenues and higher financial returns of the projects.

Another economic advantage of the previous invention is that the non-standstill of the well for chemical removal of the plaster avoids a whole chain of reflections in ongoing projects that depend on the production of the well in question, such as non-compliance and subsequent term expansion of the various phases of the project and the consequent postponement of expected financial returns, thus affecting the cash flows of these projects, eventual fines for failure to meet production targets previously committed to government regulatory agencies, contractors, business partners, investors, etc. .... which could reflect the entire operational chain of users' project portfolios with damaging consequences for financial planning and budget and cost control of the projects involved.

Claims (26)

Method for simulating a fluid for rupturing a plaster deposited on the walls of a well that penetrates an underground formation, characterized in that it comprises the following steps: a) obtaining equipment consisting of a plaster forming unit capable of facilitating forming a uniform and repeatable plaster in a filter medium under static or dynamic conditions and permitting monitoring of the fluid passing through said filter medium; b) positioning a drilling fluid in said equipment capable of forming a plaster on said filter medium of said equipment under imposed conditions of shear and differential pressure; c) plastering said filter medium while controlling the imposed shear conditions and differential pressure; d) replacing said drilling fluid with said plaster breaking fluid in said equipment; e) monitoring the flow and pressure of the plaster rupture fluid passing through said filter medium under time-stable conditions and determining the instantaneous filtration rate. Method according to claim 1, characterized in that said replacement of the drilling fluid by the plaster breaking fluid is done without significant damage to the plaster and without changing the pressure in said equipment. Method according to claim 1, characterized in that said filter medium of said equipment is constituted by a filter plug having a generally vertically arranged cylindrical wall having an inner surface and an outer surface such that at least a portion of said cylindrical wall It is formed of said filter medium and in which said filter medium can be changed to simulate different well formations. A method according to claim 3, characterized in that said equipment further comprises: a) a first chamber for said test fluid in open communication with the inner surface of said cylindrical wall; b) a second chamber in open communication with the outer surface of said cylindrical wall; (c) Equipment consisting of a plaster forming unit capable of facilitating the formation of a uniform and repeatable plaster in a filter medium under static or dynamic conditions and allowing the monitoring of fluid passing through said filter medium; Method according to claim 1, characterized in that said plaster is formed on said filter medium by applying a differential pressure along said filter medium. A method according to claim 4, characterized in that said equipment further comprises a monitor for monitoring fluid flow along said filter medium. A method according to claim 4, characterized in that said equipment further comprises a pressure gauge for measuring the fluid pressure along said filter medium. A method according to claim 5, characterized in that said equipment further comprises an axis facilitating the application of shear to said drilling fluid when forming said plaster. A method according to claim 8, further comprising removing said shaft after formation of said plaster and prior to or approximately at the time of replacement of said drilling fluid with said plaster breaking fluid. A method according to claim 9, characterized in that said equipment further comprises a guide in association with said axis such that removal of said axis from said equipment does not significantly affect said plaster. A method according to claim 9, characterized in that said equipment further comprises at least one valve in or associated with said filter medium such that said plaster is not significantly damaged if said equipment is opened. Method according to claim 1, characterized in that it comprises evaluating the effect of the variables of a drilling fluid such as viscosifier concentration, filtrate controller concentration, calcium carbonate concentration, pH, particle size and agent type. “Bridging”, gravel concentration in the fluid, lubricant concentration and permeability of the filter medium under the pressure required to rupture the plaster generated by said fluid. Method according to claim 1, characterized in that the breaking pressure of the plaster increases with increasing concentration of polymers in the fluid generating the plaster. A method according to claim 1, characterized in that the breaking pressure of the plaster decreases with increasing concentration of inert solids in the generating fluid of the plaster. A method according to claim 1, characterized in that the breaking pressure of the plaster increases with the formation of thick inner plaster and thin outer plaster. A method according to claim 1, characterized in that the breaking pressure of the plaster decreases with the formation of thin inner plaster and thick outer plaster. A method according to claim 1, characterized in that the breaking pressure of the plaster increases with increasing concentration of xanthan gum in the plaster generating fluid. A method according to claim 1, characterized in that the breaking pressure of the plaster increases with increasing concentration of filtrate controller in the plaster generating fluid. A method according to claim 1, characterized in that the breaking pressure of the plaster increases with increasing concentration of LIOVAO 4260 lubricant in the plaster generating fluid. Method according to claim 1, characterized in that the breaking pressure of the plaster decreases with the increase in calcium carbonate concentration in the THIXCARB formulation tested for the plaster generating fluid. A method according to claim 1, characterized in that for the same THIXCARB formulation, the burst pressure of the fluid generated plaster using fine calcium carbonate or mixture at a concentration of 10.0 b / bbl of glass microspheres and 25.0 Ib / bbl of medium calcium carbonate is less than the fluid-generated plaster burst pressure using baritine or medium calcium carbonate. Method according to claim 1, characterized in that the breaking pressure of the plaster generated by the THIXCARB fluid decreases with the increased permeability of the Berea sandstone. A method according to claim 1, characterized in that for low concentration of perforated solids in the plaster generating fluid, the breaking pressure of the plaster decreases with increasing concentration. A method according to claim 1, characterized in that for high concentration of perforated solids in the plaster generating fluid, the breaking pressure of the plaster increases with increasing concentration. A method according to claim 1, characterized in that for the same THIXCARB formulation, the burst pressure of the fluid generated at basic pH tends to be higher than the burst pressure of fluid generated at neutral pH or acid. System for applying a method according to claim 1, characterized in that it comprises the use of pneumatic pump (1), hydraulic fluid transfer system (2), hydraulic fluid reservoir (3), hydraulic piston (4 ), mineral oil compression chamber (5), filter plug (7), plug protection membrane (6), plug storage cylinder (8), main cylinder (11), pressure gauge (9) and plaster (10).