Moscow, August 17 - IA Neftegaz.RU.In recent decades, when drilling wells, unsupported bits with polycrystalline diamond cutters of the PDC type have been widely used.Given the high cost, reaching 1.5 million rubles, and the high productivity (driving per bit up to 14 thousand m) of PDC bits and their essential feature - maintainability, a special guide has been developed for visual assessment of PDC bit wear.In the manual, based on technical and economic indicators, all drilled bits are divided into three groups according to the degree of wear: from suitable for work, in need of repair and recyclable.Today, VNIIBT [1] and IADC [2, 3] codes are used to assess the wear of PDC bits.However, they do not consider the maintainability of the bits and are redundant in content, which makes it difficult for the operator to make an informed decision about the degree of wear of the bit and its further use.At the same time, the VNIIBT code (1978), by analogy with the earlier AAODC manual [4, 5], was chronologically developed to describe the wear of cone bits and turned out to be of little use for characterizing the wear of PDC bits.The IADC code [2, 3] as amended in 1987 is mainly intended for bit manufacturers who are improving their product, and not for consumers who are more interested in working the tool most efficiently in a given geological section and prevailing technical and technological conditions.A large number of indicators of primary and secondary types of wear that characterize the state of the bit, together with the lack of clear recommendations understandable to the expert when deciding on the suitability of the bit for further work, makes it difficult to use the IADC code for visual assessment of bit wear in field conditions.In particular, the end point of the PDC bit using the IADC code is an arbitrary decision of each operator, who relies not so much on the numerous wear indicators obtained as a result of the inspection, but on his experience, knowledge and intuition.Below is a new guide for assessing the wear of PDC bits in field conditions, which was developed on the basis of visual observations of the wear of more than two hundred bits during the provision of service support by ISK PetroEngineering LLC in the areas of Western Siberia, analysis of the mining database (defectoscopic reports, estimate documentation for bit repair, bit wear cards) and existing methods for assessing bit wear.The guide also takes into account the opinions of employees of various companies involved in the development, production and / or repair of PDC bits.A feasibility study of the initial data listed above showed that, according to the condition, all bits being worked out can be divided into three areas of wear rate: suitable for work, in need of repair and disposed of (Table 1).The position of the boundaries of the area of ​​repairable bits was found on the basis of economic calculations of the profitability of their repair.The left boundary of the area is chosen so that the cost of repair does not exceed 20 - 30% of the cost of a new bit, while maintaining the mechanical performance of the repaired bit at the level of a new one.The right one is due to the fact that, starting from a certain state of the bit, its wear progresses especially quickly, as a result of which the cost of repair reaches the cost of a new bit.Thus, when visually assessing the condition of PDC bits, it is necessary to distinguish between three main wear areas with two boundaries of the wear area of ​​repairable bits (Table 1).Economic estimates of the boundaries of the area of ​​repairable bits in Table.1 correlate with their technical characteristics.Let's describe the latter in more detail.Inspection of the bits being worked out at the drilling rig showed that it is necessary to record the wear of five main elements, indicated in order of the frequency of their influence on the final assessment of the wear of the entire bit: cutters, seats for them, flushing nozzle assemblies, bit diameter, connecting thread.Based on the experience of working out and repairing bits of ISK PetroEngineering LLC, we will consider the technological characteristics of the left and right boundaries of the element maintainability area, which must be taken into account when describing the wear of individual elements, their combination, and the entire PDC bit.1. Wear of cutters.The description of the wear of the elements should begin with the cutters, because: firstly, the wear of the cutting structure determines the presence of cutters overlapping the bottom of the well, which is necessary for successful deepening;secondly, the replacement of damaged incisors is the most expensive part of the repair;thirdly, the wear of the peripheral cutters determines the preservation of the gauge diameter;Fourthly, the description of tool wear is one of the most time-consuming stages of bit wear assessment, as it requires consideration of individual cutters, their entire set and counting the number of damaged cutters.The following characteristics of boundaries and areas of wear have been established.If during visual inspection of the cutter there are no signs of wear, then it should be considered not worn out (conditionally new).Any visible damage to the incisor, regardless of the degree and features of the nose, is sufficient to classify such an incisor as an element in need of repair.To recognize the bit as unsuitable for further work, one or more partially worn cutters are not enough.The set of all cutters should be considered, which defines the left boundary of the bit maintainability area.If the bit has more than 60% of damaged cutters out of the total set of cutters involved in the destruction of the rock, then the bit should be completed and, based on an assessment of the wear of other elements of the bit, a decision should be made to send the bit for repair or its disposal.When bits are operated with less than 40% of whole cutters, the mechanical performance of the bit decreases sharply and the intensity of wear of other elements of the bit increases up to their complete wear, when the repair of the bit is impractical.It should be noted that, regardless of the wear of the remaining elements, it was not possible to identify the right boundary of the area of ​​repairable bits only by the wear of the cutters.2. Wear of landing slots for cutters.The possibility of replacing the cutter during repair is determined not by the degree of wear of the cutter itself, but by the integrity of the seat for it in the bit body, which can be characterized by the proportion of the damaged surface of the seat.Therefore, if the surface of the seat is still completely covered by the cutter body, body and surfacing material, then the seat should be recognized as not worn out (Fig. 1a).Damage to the seat surface noted during inspection ranging from 1/10 (i.e. noticeable) to 1/2 of the initial surface area is sufficient to consider such a seat repairable, since it is still possible to install a new cutter.On fig.1b and 1c show diagrams of the characteristic partial loss of the surface of the seat for the cutter along with the lost part of the body of the cutter or the destroyed surfacing material that protects the seat.Thus, the left boundary of the repairable area of ​​the bit for the entire set of landing slots for the cutters is the destruction of 1/10 or more of the surface of at least one landing slot.In this case, the development of the bit must be completed and, based on the assessment of the wear of other elements of the bit, a decision should be made to send the bit for repair or its disposal.At the same time, it should be noted that exposure and destruction of the nest surface usually occur simultaneously.In rare cases, if a noticeable part of the nest surface is exposed, but not destroyed, such a nest should also be considered repairable.If more than half of the surface of the seat is lost (Fig. 1d), it is considered unrecoverable, since in this case it is difficult to maintain the original guide base for the orientation of the cutter when replacing it.Therefore, the right boundary of the repairable area, separating it from the area of ​​complete wear throughout the totality of the seat for the cutters, is the loss of at least one seat for more than 50% of the surface.In this case, the development of the bit must be completed and sent for disposal, regardless of the state of other elements of the bit.3. Wear of the flush nozzle assemblies.When working out the bit, it is necessary to control the presence of flushing nozzles and the absence of through washouts of the body.When the body is washed out or at least one flushing nozzle is lost, the pressure drop in the bit decreases, the rate of outflow of the flushing fluid decreases, and the cleaning of the bit and bottomhole worsens.Therefore, if the nozzle remains in its place and the body around it is not blurred, then the flushing unit should be considered not worn out.Under the through blurring of the body is understood the formation of holes in the body in addition to the flushing channels.The loss of a flush nozzle is enough to consider the nozzle assembly in need of repair.Therefore, the left boundary of the repairable wear area of ​​the bit along the nozzle assemblies is the loss of at least one nozzle without a through washout of the bit body around it.In this case, the development of the bit must be completed and, based on the assessment of the wear of other elements of the bit, a decision should be made to send the bit for repair or its disposal.When the nozzle falls out and through washout of the diameter of the original hole for it by 4 mm or more, the assembly cannot be restored and characterizes the right boundary of the repairable area of ​​the bit for the entire set of flushing nozzle assemblies.4. Bit wear in diameter.To assess the wear of bits by diameter, it is convenient to use a set of two specially made gauge rings with diameters smaller than the nominal diameter of the bit.The diameters of the first and second gauge rings are selected for each region based on the geological features of the section, the rigidity of the bottom hole assembly (BHA), the well trajectory, and taking into account the technical and technological measures planned during drilling.For example, in the fields of Western Siberia, rings smaller than the nominal diameter of the bit are successfully used - by 1% for the first and 2% for the second gauge ring.If the gauge ring No. 1 does not pass through the bit, then the bit is recognized as not worn in diameter.The passage of ring No. 1 and the failure of ring No. 2 characterize the area of ​​bits suitable for repair.In this case, the bit must be completed and, based on the wear assessment of other elements of the bit, a decision should be made to send the bit for repair or its disposal.When the gauge ring No. 2 passes through the bit, its diameter is considered completely lost and cannot be restored.This wear of the bit in diameter corresponds to the right border of the repairable area, at which the bit should be completed and it should be recommended to dispose of it regardless of the state of other elements.5. Wear of the connecting thread of the bit.To assess its wear, use the instruction manual for drill pipes [6], according to which the degree of wear of the tool joint thread is determined by the amount of tightness "H" - the distance between the stop end of the controlled bit and the template (in the form of a mating locking part manufactured in accordance with GOST 5286-75) .To determine the tightness "H", special gauges for locking threads can also be used [7].If all the threads look intact, there are no obvious gross mechanical damages, interference “H” is within the normal range, and there was no damage to the bit thread during assembly and disassembly of the BHA, then the thread is considered not worn.Any damage to the thread that does not allow the bit to be screwed on, or deviation of the “H” distance from the norm are sufficient conditions to consider the connecting thread as unsuitable for further bit operation and lying in a repairable area along the thread in which the bit must be completed and taking into account wear other elements of the bit to decide whether to send the bit for repair or its disposal.It should be noted that thread damage is rare.Under drilling conditions, the limit of complete wear of the bits on the thread was not revealed.All worn threaded connections were repaired.In table.2 summarizes the areas and boundaries of the wear of the elements and the PDC bit as a whole.During a visual inspection, all the results of observations are entered into the list of descriptions of the wear of the elements and the entire PDC bit (Table 3), and depending on the location of the elements and their combinations in the corresponding wear area, they are assigned the following code values: unworn - 0;maintainable - 1;non-recoverable – 2. The sequence of actions of the operator when assessing the wear of PDC bits: determine the first blade on the bit, based on the fact that the cutter of the first blade is located closest to the axis of the bit;sequentially check the condition of each incisor of the first blade from the central incisor to the extreme calibrating one.Each cutter is assigned one of two wear areas possible for a given element: unworn or maintainable;sequentially check the condition of each seat for the cutter on the first blade from the central cutter to the extreme calibrating one.Assign one of three possible wear areas to each seat: unworn, repairable, or beyond repair;repeat the assessment of cutter wear and cutter pockets on all remaining blades, moving clockwise;calculate the total number of cutters on the bit and the number of maintainable cutters, calculate the percentage of maintainable cutters, estimate bit wear for the entire set of cutters;to determine the availability of repairable and non-repairable cutter seats, to assess the wear of the bit over the entire set of seat seats;number flush nodes.The numbers of flushing units are assigned by successively considering the spaces between the blades, moving clockwise from the first blade.In the space between the first and second blades, the nozzle closest to the center of the bit is numbered first, if several nozzles are equally distant from the center of the bit, then they are numbered sequentially in a clockwise direction.After the completion of the numbering of the nozzles of the first interblade space, they proceed to the numbering of the nozzles of the next one, etc.;check the condition of the nozzles on the bit.Determine the number of lost nozzles, the degree of blurring of the diameter of the original holes for the nozzles, make sure that there is no blurring of the bit body, evaluate the wear of the bit over the entire set of flushing nozzle assemblies;check the bit diameter with the first gauge ring.If it passes, check the bit diameter with the second gauge ring, assess the wear;inspect the threaded connection for mechanical damage.Make sure that all threads are intact, check the tightness "H", evaluate the wear;based on the wear assessment of five elements of the bit and their combinations, give an opinion on the degree of wear of the entire bit (I);write the final PDC bit wear code in the form: P I1 (%);G I2 ;H I3 ;D I4;P I5 ;according to the degree of wear of the entire bit (I), issue a recommendation on its further use: if I = 0, then further development of the bit is recommended;if I = 1, then it is recommended to send the bit for repair;if I = 2, then it is recommended to complete the development of the bit and dispose of it.Let's consider a test example of filling the table.3. Let us describe the wear of the PDC 215.9 MS1643SS bit, which has 4 blades with a total number of cutters - 25 pieces, with a diameter of 16 and 13 mm, 6 flushing nozzles, a nominal diameter of 215.9 mm, connecting thread З-117.There are 8 incisors on the first blade, incisors Nos. 2, 3, 6, 7 and 8 are damaged, the rest are intact.The surface of the seat for cutter No. 3 is partially lost by less than half (repairable seat), the rest of the nests are intact.There are 5 incisors on the second blade, Nos. 1, 2, 4 and 5 are damaged;landing nests are intact.There are 7 incisors on the third blade, Nos. 3, 4, 6 and 7 are damaged. The surface of the seat for incisor No. 3 is completely exposed (the incisor fell out), there are damages, but less than half of the surface of the nest is lost (repairable nest), the rest of the sockets are intact.Nos. 3, 4, and 5 on the fourth lobe of five incisors are damaged;landing nests are intact.All flushing nozzles remained in their places, there are no through washouts of the bit body.When checking the diameter, the gauge ring No. 1 passes, but the gauge ring No. 2 does not.Bit wear pattern in fig.2 allows you to more clearly represent the state of the bit and its elements, described in table.3. The time sequence of several wear patterns allows you to track the dynamics of bit wear during its development and check the correctness of the bit wear description by the operator.Thus, based on the analysis of theoretical studies and field data on the operation of PDC bits, the following conclusions can be drawn: When assessing the wear of PDC bits, it is necessary to take into account their maintainability.