TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper analyzes the application of a new method for the evaluation of bit performances. At present, the most utilized methods for bit performance evaluation are mainly based on the cost-per-foot. This approach is definitely a good reference system, but it represents only a mere economic calculation, and is not well suited for keeping into account drilling difficulties due to formation variability and directional drilling conditions. The objective of the research is both the analysis of a new drilling model for bit performance evaluation, known as Bit Index (BI), and the investigation of the possibility of BI to establish sound guidelines for the development of a mathematical tool able to help during well planning, well drilling and post-well analysis. The model was tested by mining data from the Drill-Bit Catalog (DBC) prepared at the Exploration & Production Division of Eni Group (Italy). The DBC is a database that contains both parameters for the geotechnical/geomechanical characterization of the formations and bit record/performance data. Within the DBC, three wells have been identified, recently drilled in Southern Italy. These wells have been used for the comparison and evaluation of bit performances through the BI methodology. Main results allowed to identify the bits (labeled with IADC code) that drilled with the best performances in the above three wells. The proposed model, although in its early stage of development, proved to be economic and reliable. The quality of bit performance analysis obtained with this model seems also more effective than the traditional "quick look" analysis, performed on the bit records or on the pure evaluation of the cost-per-foot.
The paper is aimed to calculate an innovative numerical index for bit performance evaluation called Bit Index (BI), applied on a new type of formation and bit database also known as Formation Drillability Catalogue (FDC). A dedicated research program developed by Eni E&P Div. and the University of Bologna (Italy) studied a drilling model for drill-bit performance evaluation (the BI) derived from data recorded while drilling (bit records, master log, wireline log, etc.) that includes numerical information from dull bit evaluation. This index is calculated with data collected inside the FDC, a novel classification of formations aimed to the geotechnical and geomechanical characterization and subdivisions of the formations, called Minimum Interval (MI). FDC was conceived and prepared at Eni E&P Div., and contains a large number of significant drilling parameters. Some wells have been identified inside the FDC and have been tested for bit performance evaluation. The values of BI are calculated for each bit run and are compared with the values of the cost per meter. The case study analyzes bits of the same typology and run in the same formation. The BI methodology implemented on MI classification of FDC can improve consistently the bit performances evaluation, and it helps to identify the best performer bits. Moreover, FDC turned out to be particularly functional to BI, since it discloses and organizes many formation details that are not easily detectable or usable from bit records or master logs, allowing for targeted bit performance evaluations. At this stage of development, the BI methodology proved to be economic and reliable, helping as well to make drill bit selection less erroneous and more logical. Introduction Drill-bit performance evaluation is one of the most important issues of drilling optimization. When optimizing bit performances, drilling engineers ordinarily think in terms of factors affecting the rate of penetration, and so indirectly correlate bit performances to cost-per-meter only. This criterion, however, cannot by itself show where improvement is needed. Nowadays, drill-bit performance evaluation methods involve the development of mathematical tools along with the analysis of large number of information from various records of previously drilled wells, even though to date there is not an industry standard or a widely used methodology to address it. Bit performance evaluation and bit selection is of paramount importance for the drilling engineer. Many attempts to model and predict drill-bit selection and to evaluate their performances have been developed for a number of years. As advancements in drilling bit technology and drilling measurement systems have increased, so have the number and the sophistication of evaluation models available. Almost all the approaches are similar in objective, to make drilling bit selection less erroneous and more logical 1 and possibly free from any personal interpretation. Recently, the methods for the evaluation of bit performance improvements have not always kept the pace with technological advancements. Methods such as offset wells and cost per foot, specific energy, bit factor, formation drillability, design index and neural networks have been used for bit performance evaluation 2–10, although most of them still seem not completely satisfactory. The industry is unlikely to find a means to predict drilling without a means of relating it to some rock criteria. This study illustrates the application of an innovative mathematical tool (jointly developed by Eni E&P Div. and the University of Bologna) based on Bit Index implemented on data collected in Eni's Formation Drillability Catalogue 11–12, a data collection addressed to the geological and geomechanical classification of the formations. The method proposes a new way for using the existing information under day-to-day competitive drilling circumstances, accomplishing the desired objective at the lowest cost through the use of the most effective procedures. Finally, the paper is completed with a case study analyzing some drill-bit performances in Val d'Agri area (Southern Italy). In particular, here is presented both an application concerning the evaluation of top hole drilling in a heterogeneous formation with hard stringers, and a case of a deep and hard reservoir drilling, where a new generation of impregnated bits has been recently tested.
The paper analyzes a novel operative procedure of geological and geomechanical subdivisions of the formations, called Minimum Interval (MI). The MI concept, used in combination with other evaluation indexes, can improve consistently the evaluation of bit performances. This research compares three indexes for bit performance evaluation, i.e., cost-per-meter (CM), Specific Energy (SE) and Bit Index (BI), applied to a new type of drilling-bit database, named Formation Drillability Catalog (FDC), organized in order to implement the MI concept. Basically, the FDC is a novel classification of drilled formations conceived and prepared at Eni E&P Division (Italy), aimed to the geomechanical characterization by means of a large number of significant geological and drilling parameters, each one referred to single MI's. So far, five wells have been identified and tested for bit performance evaluation. The FDC turned out to be functional to BI, since it discloses and organizes lithostratigraphical characters that are not easily detectable or usable from bit records or master logs, allowing for targeted bit performance evaluations. Results of this case study showed that the cross correlation between BI, CM and SE can help to identify the best performer bit for each formation and for each borehole section. The quality of bit performance analyses obtained with BI and SE (through the MI concept) seems more effective than those based on CM, performed on bit records, and can also be used as a valuable tool for drill-bit selection. Cost-per-Meter, Specific Energy and Bit Index The continuously changing and more demanding needs of the drilling industry, in recent years has generated an impressive technological advancement in drilling-bit design, materials and, consequently, in their performances. Today, faster penetration rate and longer time on bottom are increasingly demanding issues for bit manufacturers, as well as reliability of both new materials and related bit performances. As advancements in drilling bit technology and drilling measurement system have increased (including while drilling measurements, instrumented bits, etc.), so have the number and the sophistication of evaluative models available, even though their application is not yet fully generalized. In the light of the above, bit performance evaluation is paramount in the process of well planning and drilling optimization. Many attempts to model and to evaluate bit performances have been developed since many years. All the approaches are similar in objective, i.e. to make drilling bit performance evaluation less erroneous, more logical and free from personal interpretation. Methods such as CM and SE have been studied, developed and applied, but not all the time with good results, especially the latter. The present research is aimed to evaluate a new drilling-bit performances indicator, named Bit Index, recently developed and tested by a joint research program existing between Eni E&P Division and the University of Bologna. In general, the most widespread and basic method for bit performance evaluation is based on the cost-per-meter (CM) of the drilled interval, calculated with equations similar to the following: Equation (1) where CM is the cost-per-meter, R the rig cost per unit time, or rig rate, T the drilling time, t the trip time, B the bit cost and F the interval drilled. Equation 1 shows that CM is controlled by five variables. For a given bit cost, CM is sensitive to changes in rig cost, trip time, drilling time and interval drilled. The trip time is not always easy to determine, while drilling time is straightforward and directly proportional to CM, provided that the other variables remain constant. Obviously, the rig rate greatly influences CM. For a given borehole section in a field that is drilled by different values of R, the same bit will produce different CM values, assuming that the same T is used in all rigs. Bit performance evaluation and bit selection carried out by means of CM is a good reference system, but it represents only a mere economic calculation, not dependent on actual drilling parameters1,2. Moreover, it is not well suited for keeping into account drilling difficulties due to formation changes (in terms of lithology and geomechanical properties) and directional drilling conditions.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe paper analyzes the application of a new method for the evaluation of bit performances. At present, the most utilized methods for bit performance evaluation are mainly based on the cost-per-foot. This approach is definitely a good reference system, but it represents only a mere economic calculation, and is not well suited for keeping into account drilling difficulties due to formation variability and directional drilling conditions. The objective of the research is both the analysis of a new drilling model for bit performance evaluation, known as Bit Index (BI), and the investigation of the possibility of BI to establish sound guidelines for the development of a mathematical tool able to help during well planning, well drilling and post-well analysis. The model was tested by mining data from the Drill-Bit Catalog (DBC) prepared at the Exploration & Production Division of Eni Group (Italy). The DBC is a database that contains both parameters for the geotechnical/geomechanical characterization of the formations and bit record/performance data. Within the DBC, three wells have been identified, recently drilled in Southern Italy. These wells have been used for the comparison and evaluation of bit performances through the BI methodology. Main results allowed to identify the bits (labeled with IADC code) that drilled with the best performances in the above three wells. The proposed model, although in its early stage of development, proved to be economic and reliable. The quality of bit performance analysis obtained with this model seems also more effective than the traditional "quick look" analysis, performed on the bit records or on the pure evaluation of the cost-per-foot.
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