SCHOLEDGE INTERNATIONAL JOURNAL OF MULTIDISCIPLINARY & ALLIED STUDIES
VOL. 2, ISSUE 6 (JUNE2015) ISSN-2394-336X
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A CRITIQUE AND REVIEW OF PETROLIUM EXPLORATION ENGINEERS� WAYS AND METHODS
Dr. Asaf Al- Ahmed
Energy Consultant
Dubai, UAE.
ABSTRACT
Recorded penetrating times may indicate critical varieties starting with one well then onto the next notwithstanding for the same aggregate boring profundity, in the same field. Aside from the development properties, boring engineers' specialized capacity assumes a noteworthy part in obliged penetrating time. Examination of penetrating execution as for already bored boring records is a typical strategy connected to evaluate if there is any requirement for a change.
A graphical procedure, known as 'expectation to absorb information investigation', is generally requested execution assessment. This methodology has two noteworthy downsides. One, there may not be sufficient number of penetrated wells to make a solid examination. This is regularly the case in a recently created field. Two, past boring practices could be performed with awful designing practices. In such a case, correlation of a given penetrating execution as for terrible designing practices does not so much demonstrate that the present practice speaks to a decent execution. This is typically the situation where already penetrated wells were done by unpracticed drillers and/or with old boring innovation.
In this paper, an alternate methodology is acquainted with survey penetrating execution, and to reduce the issues of expectation to absorb information examination. The new approach recommends that the boring rate is contrasted and a recently presented parameter, called as boring rate specialized farthest point. It will be characterized as the most extreme achievable boring rate without gambling penetrating security. This technique is better than expectation to absorb information investigation in light of the fact that; one, it doesn't rely on upon the past boring records, two, it means to bore a well at the quickest rate conceivable without endangering the security of boring operation. It has a few hindrances; one, the proposed technique can just stand up in comparison the boring rates, two, it is relentless.
The new system requires the evaluation of the operational qualities that will expand the penetrating rate. A while later, it requires the evaluation of boring rate by one of the mainstream entrance rate models. This paper discloses how to evaluate the most good estimations of key penetrating parameters, so that the boring rate can be amplified. This requires the concurrent thought of boring parameters'
numerical association with potential disappointments, and in addition their scientific association with the penetrating rate.
KEYWORDS: Petrolium Engineering, Oil Exploration, Minerals Drilling, Earth Sciences.
PRESENTATION
The rate of boring can be enhanced for a given field until it achieves its specialized point of confinement. This is the most extreme achievable boring rate (DR) without endangering boring wellbeing. The boring rate specialized point of confinement (DRTL) must be accomplished via deliberately selecting all discriminating boring parameters, which impacts DR.
A few variables influence DR [1-4]. Some of these variables are development properties, and nothing down to earth should be possible to modify them positively. Development properties, for example, pore weight, compaction, in-situ burdens and mineral substance are among the wild boring variables. Then again, a few boring variables, when chosen painstakingly, the rate of penetrating enhances essentially. Mud weight (MW), weight on bit (WOB), turning pace or pivot every moment (RPM), bit sort and water driven parameters, for example, stream rate (Q) and effect power ([F.sub.j]) are among the controllable boring variables.
NUMERICAL RELATIONSHIPS BETWEEN DRILLING RATE AND CONTROLLABLE DRILLING VARIABLES
It has long been watched that the DR for the most part increments with expanding Q [5], WOB [6], RPM [6] and fragmentary bit tooth tallness. Then again, it diminishes with expanding penetrating liquid consistency and MW [7-11]. Some of these variables may have noteworthy impacts on DR though others may have minor impacts.
A few creators have proposed numerical connections of DR with significant boring variables for moving cutter bits [12-15]. Among them maybe, the most finish numerical penetrating model being utilized is Bourgoyne and Young's model [21, 22].
DR = [f.sub.1] [f.sub.2] [f.sub.3] [f.sub.4] [f.sub.5] [f.sub.6] [f.sub.7] [f.sub.8] (1)
In the above mathematical statement the capacities [f.sub.1] through [f.sub.3] speak to the impact of wild boring variables on DR. Boring execution can't be enhanced essentially by adjusting them. Among these capacities, the capacity f1 speaks to the arrangement quality. The capacities [f.sub.2] and [f.sub.3] model the impact of compaction on infiltration rate. For instance, the capacity [f.sub.2] represents the stone quality increment because of ordinary compaction with profundity, and the capacity [f.sub.3] models the impact of undercompaction experienced in strangely compelled developments [14].
The capacities [f.sub.4] through [f.sub.8] speak to the impact of controllable penetrating variables on the DR. Case in point, the capacity [f.sub.4] models the impact of overbalance on the DR [21-22].
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)
To graphically exhibit the impact of MW on DR, Eq. 2 was substituted in Eq. 1, and DR in Eq. 1 was tackled for the information given in Table 1. Note that, the various controllable variables are kept consistent while MW was changed.
Fig. 1 shows that DR is 20 ft/hr at MW=12 ppg. On the off chance that MW is expanded to 13 ppg, the DR is chop down to 9 ft/hr. This is a decrease of more than half. Along these lines, from the viewpoint of DR, it is imperative to choose MW as light as would be prudent. Consequently, it is vital to focus the base MW, which won't prompt whatever other penetrating issue.
In Eq. 1, the capacities f5 and f6 model the impacts of WOB and RPM on the DR [21-22].
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (3)
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (4)
WOB versus DR graph (Fig. 2) can be created comparably, by substituting Eq. 3 in Eq. 1, and tackling for DR from the subsequent mathematical statement. Once more, the information in Table 1 is utilized to deliver Fig. 2, be that as it may, in this specific case, while evolving WOB, the accompanying variables were kept consistent: RPM, [F.sub.j], h, MW.
RPM versus DR graph (Fig. 3) is created comparably, by substituting Eq. 4 in Eq.1, and by tackling the subsequent mathematical statement for DR. For this situation, in any case, DR information is figured at distinctive estimations of RPM by keeping every other variable consistent, for example, WOB, [F.sub.j], h, MW. Not surprisingly, Fig. 2 & 3 show that DR increments with expanding WOB and RPM. In this manner, it is critical to focus the most extreme reasonable estimations of WOB and RPM for a given borehole condition and tubular setup.
When all is said in done, the DR increments with expanded bit water power and Q. Notwithstanding, once the base of the opening underneath the boring tool is proficiently wiped off cuttings, a further increment in the Q (and/or [F.sub.j]) is only a waste.
The capacity f8 models the impact of bit power through pressure on DR [21-22].
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (5)
The Q identifies with [F.sub.j] with the accompanying comparison:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (6)
The DR for a given Q can be ascertained as taking after. [F.sub.j] is figured from Eq. 6 for a given Q. At that point, ascertained [F.sub.j] is substituted in Eq. 5 to focus capacity [f.sub.8], which thusly, is substituted in Eq. 1 to focus the DR.
Fig. 4 outlines the relationship between the Q and the DR. As said some time recently, take note of that once a proficient cleaning is accomplished at the base of the bit, a further increment in Q won't enhance DR more. This is delineated in Fig. 4 with two different bends, which relate to two different 'suggested effect power per square crawl of base opening territory' values. These are 9 and 12 lbf/[in.sup.2] individually. The lower bend shows that the successful base gap cleaning can be accomplished at 130 gal/min which relates to [F.sub.j]=9 lbf/[in.sup.2], and the upper bend demonstrates that the compelling base gap cleaning can be come to at around 150 gal/min, which compares to [F.sub.J]=12 lbf/[in.sup.2]. Note that, Eq. 6 can be utilized to focus the obliged Q for a given 'suggested effect power per square creep of base gap region.' This information is gotten either, in the research center with the lab tests, or at the field with drill off test.
The capacity [f.sub.7] models the impact of tooth wear (h) on the DR [21-22].
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (7)
By substituting [f.sub.7] into Eq. 1 and utilizing information as a part of Table 1, DR was computed and plotted as in Fig. 5 for h qualities running from h=0/eighth (for another bit tooth) to h=8/[8th (completely exhausted bit tooth). Not surprisingly and represented in Fig. 5, DR is conversely corresponding with the estimation of h.
PENETRATING RATE TECHNICAL LIMIT
As a rule, if lighter MW, heavier WOB, speedier RPM and higher Q are utilized, the normal result is quicker DR. Fig. 7, created by utilizing Eq. 1 and the information in Table 1, exhibits this graphically. Fig. 7 shows that the DR of 22 ft for each hr can be come to if controllable boring parameters are chosen as given under the upper must line. In any case, it doesn't imply that the most extreme achievable DR is 22 ft for every hr. It just exhibits how DR enhances as basic penetrating parameters changes positively. Clearly, if the MW is decreased underneath 12 ppg, the WOB is expanded over 40K lbf, and the RPM is expanded more than 100, the new DR line on the same chart will fall over the upper most line. It is imperative to note that, once the Q ranges to 200 gal for every min, the DR does not increment any longer with expanding Q, as this quality relates to suggested effect power of 9 lb for every square creep of base opening territory which is required for a compelling cleaning of gap underneath the stone bit.
Presently to survey the greatest achievable DR, which can likewise be called as the boring rate specialized point of confinement (DRTL), taking after inquiries must be replied. These are:
1. What is the base worthy MW?
2. What is the most extreme adequate WOB and RPM?
3. What is the most extreme prescribed Q?
4. What will be the boring rate or DRTL, if penetrating parameters are situated as above qualities?
Surveying Controllable Drilling Variables to Reach Drtl
Honing designers can enhance their boring productivity altogether via precisely selecting controllable boring variables. Nonetheless, these variables can't be chosen exclusively taking into account DR without thinking of it as' result on the wellbeing of boring operation.
For a given boring case, there exists an upper and a lower viable utmost of each controllable penetrating variable. These points of confinement can be dictated by selecting the controllable boring variables at their most ideal values that won't bring about any potential disappointment. This requires the expectation of potential disappointment, and also its scientific association with the suitable boring variable.
The accompanying boring variables will be examined; MW, WOB, RPM and Q
MUD WEIGHT
It has been expressed that the boring liquid is likely the most imperative variable to be considered in penetrating enhancement and water power is the second [16]. Boring liquid thickness or MW has a significant impact on the DR. It is one of the variables contrarily corresponding to the DR. It has been watched that the DR for the most part increments with diminishing equal coursing thickness (ECD). One approach to diminish ECD is to lessen the MW, and the other is to decrease its thickness.
All in all, what is the base MW so that penetrating operation is no in threat? The response to this inquiry can be gotten by researching the conceivable issues that can be expected because of lacking MW. The accompanying two boring issues may emerge in view of lacking MW:
1. Arrangement liquids may stream into the borehole (kick),
2. The borehole may crumple (arrangement precariousness).
These two issues generally show up at two diverse MWs. Subsequently, the most minimal worthy penetrating liquid thickness will be the higher one of the two qualities. This guarantees that both issues don't appear amid penetrating.
While penetrating a porous development, arrangement liquids may stream into the borehole if the boring mud hydrostatic weight falls underneath the development liquid weight. In such a case, the lower furthest reaches of boring liquid thickness is chosen in a manner that the hydrostatic weight of the mud segment is marginally higher that the development liquid weight (around 150 psi). Hence, the lower furthest reaches of development liquid thickness, MW, is resolved basically by:
MW = [P.sub.f] + 150/0.052 D (8)
Development breakdown or arrangement compressive disappointment is a kind of the borehole shakiness, which rises when lacking mud weight is being used amid the penetrating of touchy developments [17-18]. To figure out if compressive disappointment will happen at borehole divider for a given mud weight, the anxiety state characterized by two variables octahedral shear stress, [[tau].sub.oct] and compelling limiting weight, ([P.sub.c]-[P.sub.f])- - is contrasted and a tentatively decided rock disappointment envelope [19], for example, that indicated in Fig. 6. In the event that the anxiety state at the borehole divider falls beneath the stone quality bend, as at focuses An and C in Fig. 6, it is expected that compressive disappointment won't happen, something else, the borehole divider will disintegrate and breakdown.
For the accepted state of no stream, vertical well and ordinarily focused on development the anxieties at the borehole divider are given in polar arranges by;
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (9)
[[sigma].sub.r] [P.sub.m] = MW D (10)
[[sigma].sub.[theta]] = 2[[sigma].sub.H] - [P.sub.m] = 2[[sigma].sub.z](v/1 - v) - MW D (11)
As far as [[sigma].sub.r], [[sigma].sub.[theta]], [[sigma].sub.z] the compelling keeping weight and the octahedral shear anxiety are given by:
[P.sub.c] - [P.sub.f] = [[sigma].sub.[theta]] + [[sigma].sub.z] + [[sigma].sub.r]/3 - [P.sub.f] (12)
[[tau].sub.oct] = [square foundation of ([([[sigma].sub.[theta]] - [[sigma].sub.r]).sup.2] + [([[sigma].sub.[theta]] - [[sigma].sub.z]).sup.2] + [([[sigma].sub.z] - [[sigma].sub.r]).sup.2]/6)] (13)
Subsequently, once a tentatively delivered rock disappointment envelope is acquired, for a given successful limiting weight, the base mud thickness can be resolved as taking after:
1. ([P.sub.c] - [P.sub.f]) is computed from Eq. 12.
2. [[tau].sub.oct] is resolved from Fig. 6.
3. At last, MW is comprehended from Eq. 13 subsequent to substituting MW D for [[sigma].sub.r] and
2[[sigma].sub.z](v/1 - v) - MW D for [[sigma].sub.[theta]]
In situations where no research facility information is accessible for deciding a stone disappointment envelope, the accompanying experimental connections can be utilized to figure out if the stone comes up short or not [20,21].
The uniaxial compressive quality is computed from mass thickness, shear and compressional sonic speeds and gamma beam information.
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (14)
Poisson's proportion, ?, can be experimentally decided from shear and compressional sonic speeds as in the accompanying mathematical statement:
v = 1/2 [([[DELTA][t.sub.s]/[[DELTA][t.sub.c]).sup.2] - 1/[([[DELTA][t.sub.s]/[[DELTA][t.sub.c]).sup.2]-1 (15)
When the estimation of [C.sub.o] is resolved experimentally, then it can be brought into Coulomb's standard, to figure out if the stone comes up short or not under present borehole stress, it can be expressed as takes after:
[C.sub.o] = ([[sigma].sub.max] - [P.sub.f])- [([square foundation of ([v.sup.2] + 1 + v).sup.2] ([[sigma].sub.min] - [P.sub.f]) (16)
For an ordinarily pushed, tectonically idle development where most extreme and least flat anxieties are equivalent, it is sensible to accept that [[sigma].sub.max]=[[sigma].sub.z] and [[sigma].sub.min]=[[sigma].sub.[theta]]. Henceforth, by consolidating Eq. 9 through Eq. 16, the most reduced MW that fulfills the mechanical borehole dependability criteria can be resolved from the accompanying relationship:
MW = 1/D[2[[sigma].sub.H] - [P.sub.f] - [[sigma].sub.z] - [P.sub.f] - [C.sub.o]/([square foundation of [([v.sup.2] + 1 + v)).sup.2]] (17)
WEIGHT ON BIT
One of the real variables, which altogether influences DR, is the WOB. Given that there is effective base opening cleaning underneath the bit teeth, for the most part, the DR increments with expanding WOB. Then again, as on account of numerous controllable boring variables, there is a furthest point of confinement of WOB that must not be surpassed. The maximum furthest reaches of WOB is chosen in the wake of taking after two basic burdens are resolved:
1. The WOB at which the bit drills at least cost
2. Discriminating Buckling Load (CBL) of drill string.
The first of the over two guarantees that working expense of boring apparatus is busy's base quality. Notice that the base expense WOB does not guarantee that the DR is grinding away's most extreme. This is thought to be one of the key necessities of financially savvy boring. Hence, if the DR is to be expanded as an objective, then minimizing expense per foot criteria can be yielded.
In the event that adequate information is accessible to deliver a table of bit working cost as a component of WOB and RPM, then graphical procedure can be utilized to focus the base expense WOB and RPM [22]. Be that as it may, without such a table, a few diagnostic routines can be utilized. There are two famous logical models that can be utilized to create a table of 'expense per foot' for a scope of down to earth WOB and RPM [12-15]. They are both used to show DR for tri-cone roller cone bits. When the expense per footage table is developed, the base expense per footage and relating estimations of WOB and RPM can without much of a stretch be recognized.
Least cost WOB does not ensure that under such WOB the current drill string will be mechanically steady. Along these lines, once the base expense WOB is resolved, the security of those channels must be explored. In the event that the base expense WOB needs more pressure than the discriminating clasping burden (CBL) of drill collars, than the greatest estimation of WOB must be decreased to CBL of the drill collars.
Amid the boring of even and amplified achieve wells, once in a while, drill channels must be put in pressure to accomplish the obliged WOB. For this situation, the CBL of drill funnels must be resolved and added to the longitudinal segment of drillcollar weight to focus the most extreme pertinent WOB from the stance of drill string steadiness.
The accompanying mathematical statement can be utilized to appraise the CBL of channels in slanted and straight gaps [23-27].
CBL = 1,617 [square foundation of ([B.sub.f]([OD.sup.2] - [ID.sup.2])([OD.sup.4] - [ID.sup.4])Sin [beta]/(H-OD)) (18)
It is worth to specifying that the CBL of funnels can be expanded considerably, if stabilizers are appended to pipes. In such cases the quantity of stabilizers, as well as the area of stabilizers inside of the string decides the estimation of CBL [32].
ROTATIONAL SPEED
Rotational Speed or RPM is among the controllable variables that fundamentally influence the DR. Accepting that base opening cleaning is satisfactory, DR for the most part increments with expanded RPM. Then again, in most commonsense applications, the ideal RPM is chosen so that per footage expense of penetrating is at least. This is called least cost revolving rate (NMC). This number and least cost WOB can be resolved at the same time [12-15]. Be that as it may, before applying least cost RPM, the torsional quality of channels must be explored. In the event that base expense RPM will put drill pipes in helical clasping mode before it reaches to boring tool, than the greatest safe RPM must be controlled by considering the torsional quality of drill funnel.
Drill funnels will torsionally clasp if torsional burdens surpass the base torque needed to clasp them. The clasping quality of a drill channel against torsional burden relies on upon the amount of pressure or pressure is set on it. The accompanying equation can be utilized to focus the torsional resistance of a tubular under a given pressure or pressure [22].
[[tau].sub.r] = [square base of (833,333 [I.sub.p](2,056,168[I.sub.P]/[L.sub.P.sup.2]+F)) (19)
The boring tool hang-up and Bottom Hole Assembly (BHA) rotational drag are thought to be the two elements, which cause drill channel helical clasping. The accompanying BHA torsional model predicts the transmission of torsional burdens made by the bit through the drill collars and afterward into the drill funnel [28].
[tau] = 0.795 [N.sub.HU] [J.sub.p][2 [J.sub.c]/[J.sub.c] + [J.sub.p]] (20)
By substituting [[tau].sub.r] from Eq. 19 into [tau] in Eq. 20, one can tackle for the most extreme estimation of rotational velocity ([N.sub.HU]) that can be connected to keep away from helical locking of drill pipes on the off chance that the bit hangs-up.
Torsional clasping of the drill funnels might likewise be foreseen if the data torque by the rotating table is unreasonable. The accompanying mathematical statement utilizes watts devoured by an electric rotational commute to gauge the drill channel torque by the turning framework [24].
[tau] = 7.04 V I eff mff/[N.sub.RD] [[eta].sub.BHA] (21)
So also, by substituting [[tau].sub.r] from Eq. 19 into [tau] in Eq. 21, one can fathom for the most extreme estimation of revolving velocity ([N.sub.RD]) to maintain a strategic distance from drill channel helical clasping.
At long last, among the three turning rates, [N.sub.MC], [N.sub.HU] and [N.sub.RD], the littlest one is chosen as the most extreme appropriate RPM.
COURSE RATE
Research center and field boring tests demonstrate that the DR ascends with expanded bit power through pressure to a most extreme worth and from there on neglects to bring about a further ascent [29]. This wonder is translated to imply that once the base of the gap is cleaned that further endeavors at cleaning are a misuse of bit hydrodynamics (Fig. 7). In this manner from the outlook of bit power through pressure, the Q can be expanded until penetrating liquid completely cleans the cuttings underneath the bit. On the other hand, this rate may not be sufficient to course cuttings out of the opening. Higher Q is regularly expected to anticipate cuttings bed development in slanted and even wells.
The accompanying recipe can be utilized to discover the Q, which expands bit water driven torque (BHHP) with the requirement of a chose Bit pressure driven pull per square creep of base gap territory [30].
Q = [[1714 BHHP/j m].sup.(1/m+1)] (22)
Essentially, the accompanying recipe can be utilized to discover the Q, which expands plane effect power ([F.sub.j]) with the imperative of a chose effect power for each square crawl of base gap zone (30).
Q = [[[6,649.35F.sub.j.sup.2]/j m MW].sup.(1/m+2)] (23)
On the off chance that the Q expected to improve bit water power is deficient for effective borehole cleaning then full transport Q must be chosen as the base Q. The accompanying recipe was proposed to focus the full transport Q in directional wells [31].
Q = [pi]/4([H.sup.2] - [OD.sup.2])[([V.sub.1]Cos[beta]) + ([V.sub.2]Sin[beta])] (24)
[V.sub.2] = 44[[[(SW - MW/MW)[g.sup.3](H - OD/12).sup.3]].sup.1/6] (25)
Eqn's. 24 and 25 are utilized to develop full transport annular Q outline (Fig. 8). The obliged Q is chosen by entering the diagram with opening slant ([beta]).
CONCLUSIONS
DR unequivocally relies on upon a few controllable boring variables. Fitting determination of these variables can essentially enhance the DR. On the other hand, there is a furthest cutoff of DR, which can't be surpassed without taking a chance with the security of penetrating operation. This rate is known as the boring rate specialized utmost and can be drawn closer if:
* MW is chosen as the greater of taking after two values; a) base MW expected to counteract development liquid kick, and b) least MW expected to forestall borehole breakdown.
* WOB is chosen as the littler of taking after two values; an) ideal WOB for least cost per footage, and b) least discriminating clasping heap of drillstring parcel that will be put in pressure.
* RPM is chosen as the littlest of taking after three values; a) most extreme reasonable RPM for rotational drag, b) greatest suitable RPM for bit hang up, c) ideal RPM for least cost per footage.
* Q is chosen as the greater of taking after two values; a) base stream rate expected to avert cuttings bed arrangement in slanted gaps and vertical openings, b) the stream rate requirement for a successful cleaning underneath the bit tooth.
When controllable boring parameters are resolved as above, and the DR is figured by one of the penetrating rate models, boring specialists will have the capacity to assess their boring execution with a superior instrument, as opposed to utilizing excellent learn bend investigation strategy which is accepted to have significant downsides.
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