Estimating the drilling rate in Ahvaz oil field

Transcription

1 J Petrol Explor Pro Technol (2013) 3: DOI /s ORIGINAL PAPER - PRODUCTION ENGINEERING Estimating the rilling rate in Ahvaz oil fiel Masou Cheraghi Seifaba Peyman Ehteshami Receive: 28 December 2012 / Accepte: 5 May 2013 / Publishe online: 25 May 2013 The Author(s) This article is publishe ith open access at Springerlink.com Abstract Optimizing the rilling operations epens on an unerstaning of the interaction beteen the rilling equipment an the geological formations at any given site an a reasonable estimation of the rate of rilling, given the operational parameters use in rilling. Therefore, it is very important to evelop a moel for estimation of the rilling rate, using the groun an operational parameters of the rill. These moels provie for accurate preiction of achievable rates, time for the ell completion an rilling costs as ell as optimization of such crucial parameters as eight on the bit an the rotary spee. This paper ill aress the parameters affecting oil ell rilling an uses the information from 50 oil ells in Ahvaz oil fiel to offer empirical equations for estimation of the rilling rates in relate geological formations. Keyors Oil fiel Drilling rate Moeling Rock formations Introuction Due to relatively high cost of rilling operations, it is essential to evelop an accurate preiction of rill performance an rilling rate to estimate the time neee for completion of a ell an the relate costs. Previous stuies sho that a small portion of the total rilling time is spent on actual rock cutting in the all by the bit, an the rest is the ontime components that inclue traversing the ros in an out of the ell. Obviously one of the ays to improve M. C. Seifaba (&) P. Ehteshami Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran cheraghi@cc.iut.ac.ir the operation is to increase the bit efficiency an ecrease rill ontime. Increasing the rilling efficiency means increasing the rilling rate by optimizing the combination of eight on bit (WOB) an rotational spee for the given bit in a given rock formation as ell as increasing the ratio of rilling to bit trip time. In other ors, increase rilling spee an higher number of hours spent on rilling as oppose to travel time results in higher rilling rate per ay. This requires a goo knolege of the parameters controlling the rilling operation an the life of the rill bit. In-epth stuy of the various rilling systems an their performance in a given site or region is the builing block for improving the rilling operations. Such a stuy requires goo recor-keeping an relies on accurate recors of rilling operations to evelop a atabase of various parameters that can affect the rilling rates. Analysis of fiel ata allos an engineer to moel the relationship beteen the rilling rates an the relate parameters. Therefore, application of moels for preiction of the rilling rate is necessary for (1) preiction of the time neee for rilling a ell ith a given size an specifications in a knon group of rock formations an (2) selection of the optimum WOB an rotational spee of bit to increase the rilling rate. In the past 40 years, the researchers have introuce various moels to preict the rilling rate. This inclues the ork by Bourgoyne an Young (1974, 1999) Bourgoyne et al. 2003; Maurer (1962); Cunningham (1978); Walker et al. (1986); Warren (1987); an Kahraman (1999). A number of the moels ere evelope base on laboratory testing an others by fiel observations. Since the ifferent parameters affect the rilling rate an the role of each parameter is not specifically efine, the nee for a suitable metho ith a goo level of accuracy is felt in all the areas. For this reason, the present stuy examine first a moel of the rilling rate preiction in Ahvaz oil fiel. In

2 170 J Petrol Explor Pro Technol (2013) 3: oing so, the available relationship ith the possibility of these moels as specifie to optimize the oil ell rilling operation for future in Iran. The stuy use the bit ata of 50 oil ells for moeling. Depening on the ata, the number of effective parameters on the rilling rate presents a moel utilizing multiple regression analysis. Minitab as use to apply regression analysis. This mae it possible to etermine the moel correctly accoring to its capabilities. By consiering the iversity of the rocks, variable conitions of rilling ith ifferent formations an inaequate ata from the physical an mechanical properties of rocks, the iea as to reuce the ata to fin accurate an extenable results. Therefore, it as ecie to introuce the moels base on the formations. Drilling rate preiction moels A number of the effective parameters on the rilling rate are as follos: loa on bit, rotation, epth, rock strength, bit conition, formation pressure, mu eight, mu type, bit iameter, an mu flo rate (Bourgoyne an Young 1974). In each of the present moes, epening on laboratory or operational conitions, only a number of the effective parameters on oil ell rilling ere employe. This coul lea to minor mistakes hich, hoever, seem unavoiable. Bourgoyne an Young s moel This moel as introuce in 1974 an coul count as one of the best. Al-Betairi et al. (1988) suggestion for the rilling rate preiction in the Persian Gulf base as it is on Bourgoyne an Young s moel as successful. Bourgoyne moel is as follos: ln R¼a 1 þ X8 j¼2 a j x j ð1þ x 2 ¼ D ð2þ x 3 ¼ D 0:69 g p 9 ð3þ x 4 ¼ D g p q c ð4þ X 5 ¼ ln! t 4 ð5þ t N x 6 ¼ ln ð6þ 100 x 7 ¼ h ð7þ x 8 ¼ qq 35ol n ð8þ R = Drilling rate (ft h -1 ), D = ell epth (ft), g p = pore pressure graient (lb gal -1 ), q c = equivalent mu ensity (lb gal -1 ), = eight on bit (1,000 lb in-1 ), = threshol bit eight per inch of bit iameter t (1,000 lb in -1 ), N = rotary spee (rpm), q = mu ensity (lb gal -1 ), q = flo rate (gal min -1 ), l = the apparent viscosity at 10,000 s -1 (cp), n = bit nozzle iameter (in), h = Fractional tooth height orn aay Using this moel requires a efinition of a 1 to a 8 coefficients epening on the area chosen an the relate ata. Consequently the moel is useful for a specific area. Various moels have also been introuce by other investigators in the fiel. Hoever, it is commonplace that each moel consiers only some of the effective parameters an ignores others. Consequently, each moel may be vali in one area but not in others. Therefore, the final ecision is to introuce a variety of moels in the Ahvaz oil fiel area. Geological conitions Ahvaz oil fiel is locate in Ahvaz (southeast of Iran). The formations are rille as follos: Agha Jari formation This consists of bron to grey limy sanstones, re marls ith veins of gypsum an re siltstone. Gachsaran formation This consists of anhyrite, re marl, grey marl an little limestone. Asmari formation This inclues carbonate an sany facies associate ith a little shale. Sarvak formation This contains cream to bron limestone an shale. Data processing The rilling rate preiction moels are evelope by both laboratory an fiel ork. The laboratory moels emboy not only the physical an mechanical properties but also the accurate measurements as they cannot simulate the real conitions. Therefore, they are inefficient. But the empirical moels are more epenable an efficient than laboratory moels because they are mae uner real conitions. Generally the moels are epenable an usable for a specific rock type formation. Thanks to the avantages of the empirical over the laboratory moels, a ecision as mae to introuce a moel for preiction of the rilling rate in the Ahvaz oil fiel area base on the empirical ata. Type of ata The ata are illustrate in terms of bit characteristics: bit number, bit size, make, bit type, nozzle size, epth an eviation, eight on bit, rotation, pump pressure, mu flo rate, mu eight, mu viscosity, an bit conition.

3 J Petrol Explor Pro Technol (2013) 3: Table 1 Parameters affecting Agha Jari moel Bit iameter (in) 17.5 Bit rotation (rpm) Weight on bit (1,000 lb) Depth (m) ,741.5 Mu ensity (pcf) Mu viscosity (s) ROP ¼ e ð4:04þ0:00458nþ0:0147w 0:00101D 0:0248MW 0:0169MV 0:0375TÞ R 2 P ¼ 85:7 % Table 4 Parameters affecting Sarvak moel Bit iameter (in) Bit rotation (rpm) Weight on bit (1,000 lb) 5 25 Depth (m) 3,404 4,139.5 Mu ensity (pcf) Mu viscosity (s) ROP ¼ N 0:65 W 0:25 ð 2:26 0:00212 FROMþ0:00251 TO 0:0463MV 0:0120TÞ e R 2 P ¼ 67:2 % Table 2 Parameters affecting Gachsaran moel Bit iameter (in) 17.5 Bit rotation (rpm) Weight on bit (1,000 1b) Depth (m) 1, ,075.5 Mu ensity (pcf) Mu viscosity (s) ROP ¼ 8:83 þ 0:00805Nþ0:0427W 0:00162D 0:0843MV R 2 P ¼ 77:2 % Table 3 Parameters affecting Asmari moel Bit iameter (in) Bit rotation (rpm) Weight on bit (1,000 1b) Depth (m) 2,511 2,820.5 Mu ensity (pcf) Mu viscosity (s) ROP ¼ N 0:6 W 0:25 ð0:58 0:00209 FROMþ0:00158 TO 0:0199MW 0:0124MV 0:0574TÞ e R 2 P ¼ 73:3 % The moeling proceure A esirable moel for the rilling rate preiction is one hich can be employe in ifferent areas. Therefore, the moeling is esigne base on the formation characteristics. It shoul be remine that ifferent bits are not treate ientically for a specific formation an that performance epens on the bit structure. Hence, it as ecie to use relatively similar bits in the moels, e.g., the bit ata ere selecte ith no big ifference in their structure an International Association of Drilling Contractors (IADC). This as one to reuce the number of the moels an facilitate their use. In aition, provie the effect of the type an number of ifferent factors are note, the reason for the cases selecte ill be clarifie. Thus, if the bit rotation or the loa on the bit is zero, the rilling rate must also be zero; otherise, the rilling operation ill stop. Nevertheless, in the present stuy the effect of mu specific gravity, mu viscosity, epth, bit iameter, bit rotation, eight on bit completely epens on rilling operations. Therefore, these epen on the type an parameters of the rilling rate. For each formation the coefficient of ajuste etermination as examine. Hypothetical regression tests ere run an graphs ere plotte to present the actual an preicte values using the moel in ifferent cases. This resulte in selecting the most useful moel. The ifferent moels are as follos (for the proceure of regression analysis reference is mae to Wittink s book, 1992): ROP = A 1 þa 2 NþA 3 WþA 4 MW + A 5 MV + A 6 TþA 7 D ð9þ ln ROP ¼ A 1 þ A 2 N þ A 3 W þ A 4 MW þ A 5 MV þ A 6 T þ A 7 D ð10þ ROP ¼ A 1 +A 2 lnnþa 3 lnwþa 4 lnmw + A 5 lnmv þa 6 lntþa 7 lnd ln ROP ¼ A 1 þa 2 lnnþa 3 lnwþa 4 lnmw + A 5 lnmv þa 6 lntþa 7 lnd ROP N a W b ¼ A 1þA 2 MW + A 3 MV + A 4 TþA 5 D ln ROP N a W b ¼ A 1þA 2 MW + A 3 MV + A 4 TþA 5 D ROP N a W b ¼ A 1þA 2 lnmw + A 3 lnmv + A 4 lntþa 5 D ln ROP N a W b ¼ A 1þA 2 lnmw + A 3 lnmv + A 4 lnt + A 5 D ð11þ ð12þ ð13þ ð14þ ð15þ ð16þ A j = The coefficients epen on the type of formation, ROP = rilling rate (m h -1 ), N = rotary spee (rpm), W = eight on bit (1,000 lbs), MW = mu eight (pcf), MV = mu viscosity (s), T = bit conition (ne bit or ol

4 172 J Petrol Explor Pro Technol (2013) 3: Fig. 1 Relation beteen actual an preicte rilling rate in Agha Jari moel Fig. 3 Relation beteen actual an preicte rilling rate in Asmari moel Fig. 2 Relation beteen actual an preicte rilling rate in Gachsaran moel one etermine experimentally by rilling engineer), D = epth (m), From = the epth hen rilling is initiate, To = epth on completion of rilling. Drilling rate preiction moels in Ahvaz oil fiel area In this section, the rilling rate preiction moel is introuce for four formations, Agha Jari, Gachsaran, Asmari an Sarvak. As the rilling rate conitions an parameters affecting them are similar for all the formations, the errors available for ifferent moels are relatively ientical. This is significant in formations ith a lo rilling rate. It ecreases the moel accuracy. Compare ith Agha Jari moel, Gachsaran, Asmari an Sarvak have lo accuracy ue to the lo rilling rate. In each of the moels introuce, first the bit types are iscusse an then Tables 1, 2, 3 an 4 shoing the range of effective parameters are introuce. Thus, the actual an preicte values of the Fig. 4 Relation beteen actual an preicte rilling rate in Sarvak moel relate moels are represente in graphs (Figs. 1, 2, 3, 4) along ith the coefficient of ajuste etermination. Conclusion The present stuy as conucte on rilling operations in Ahvaz oil fiel an resulte in the folloing: (1) the sequence of layers in the manner an the epth available can preict the approximate bounaries of formations. Thus, the moels introuce in Ahvaz oil fiel are both usable an generalizable. (2) The moels introuce can preict the rilling rate an hence the time of the rilling operation an the expenses (i.e., the cost of rilling rig an other). Therefore, it is possible to use these moels to choose the optimum eight on the bit an bit rotation. Acknolegments The authors oul like to thank the rilling staff of National Iranian Oil Company (Southern Oil Fiels) for their contribution an cooperation in this research.

5 J Petrol Explor Pro Technol (2013) 3: Open Access This article is istribute uner the terms of the Creative Commons Attribution License hich permits any use, istribution, an reprouction in any meium, provie the original author(s) an the source are creite. References Al-Betairi EA, Moussa MM, Al-Otaibi S (1988) Multiple regression approach to optimize rilling operations in the Arabian Gulf area. SPE Drill Eng 3(1):83 88 Bourgoyne AT, Young FS (1974) A multiple regression approach to optimal rilling an abnormal pressure etection. SPEJ 14(4): Bourgoyne AT, Young FS (1999) A multiple regression approach to optimal rilling an abnormal pressure etection, society of petroleum engineers. SPE Reprints Series 49:27 40 Bourgoyne AT, Millheim KK, Chenevert ME, Young FS (2003) Applie rilling engineering. SPE, Richarson Cunningham RA (1978) An empirical approach for relating rilling parameters. JPT 30(7): Kahraman S (1999) Rotary an percussive rilling preiction using regression analysis. Int J Rock Mech Min Sci 36(7): Maurer WC (1962) The perfect-cleaning theory of rotary rilling. JPT 14(11): Walker BH, Black AD, Klauber WP, Little T, Khoaverian M (1986) Roller bit penetration rate response as a function of rock properties an ell epth, SPE Warren TM (1987) Penetration rate performance of roller cone bits. SPE Drill Eng 2(1):9 18 Wittink Dick R (1992) The application of regression analysis. Prentice Hall, USA