Temperature Regime of Boreholes: Cementing of Production Liners

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1 PROCEEINGS, Thirty-Ninth Wrkshp n Gethermal Reservir Engineering Stanfrd University, Stanfrd, Califrnia, February 4-6, 014 SGP-TR-0 Temperature Regime f Brehles: Cementing f Prductin Liners Izzy M. Kutasv 1, Lev V. Eppelbaum 1 BYG Cnsulting C, Bstn, USA ept. f Gephysical, Atmspheric and Planetary Sciences, Raymnd and Beverly Sackler Faculty f Exact Sciences, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel Keyrds: shut-in temperature, mud circulating temperature, liner cementing ABSTRACT The effect f the brehle temperature recvery prcess effects (disturbed by drilling peratins) the technlgy f the casing cementing peratins. The design f cement slurries becmes mre critical hen a casing liner is used because the perfrmance requirements shuld be simultaneusly satisfied at the tp and at the bttm f the liner. Fr these reasns it is lgical t assume that the bttmhle shut-in temperature shuld be cnsidered as parameter in the cement slurry design. In deep ells the actual dnhle temperature during cement setting may significantly differ frm the mud circulating r frm the frmatin (undisturbed) temperatures. In this paper e suggest t methds (an empirical equatin, the equivalent API Wellbre methd). An early develped relatinship can be used t determine the shut-in temperatures. A field example is presented t demnstrate the calculatin prcedure. 1. INTROUCTION In this paper e ill cnsider the effect f the brehle temperature recvery prcess (disturbed by drilling peratins) n the prductin liner cementing casing. Temperature and pressure are t basic influences n the dnhle perfrmance (Eppelbaum and Kutasv, 006) f cement slurries. They affect h lng the slurry ill pump and h it develps the strength necessary t supprt the pipe. Temperature has the mre prnunced influence. The dnhle temperature cntrls the pace f chemical reactins during cement hydratin resulting in cement setting and strength develpment. The shut-in temperature affects h lng the slurry ill pump and h ell it develps the strength t supprt the pipe. As the frmatin temperature increases, the cement slurry hydrates and sets faster and develps strength mre rapidly. Cement slurries must be designed ith sufficient pumping time t prvide safe placement in the ell. At the same time the cement slurry cannt be verly retarded as this ill prevent the develpment f satisfactry cmpressive strength. The thickening time f cement is the time that the slurry remains pumpable under set cnditins. The specificatins f circulatin temperature in the design f thickening times fr il ell cement are very imprtant. While retarders can extend thickening times, the thickening time fr a given cncentratin f retarder is still very sensitive t changes in temperature. Slurries designed fr errneusly high circulating temperatures can have unacceptably lng setting times at ler temperatures. A cmpressive strength f 500 psi (in 4 hurs) is usually cnsidered acceptable fr casing supprt (Rmer and Lizz, 000). Frm Figure 1 flls that a temperature difference f nly 6 F (3.3 C) significantly affects the cmpressive strength develpment f the cement. T reduce the ait n cement e recmmend increasing the utlet mud temperature. Earlier e suggested this technique t reduce ait n cement at surface casing fr ells in permafrst regins (Kutasv, 1999). This may reduce the cst assciated ith cementing f the cnductr and surface casing. Figure 1: Cmpressive strength develpment fr a deep-ater The design f cement slurries becmes mre critical hen a casing liner is used because the perfrmance requirements shuld be simultaneusly satisfied at the tp and at the bttm f the liner. Frmatin (undisturbed) temperatures and fluid circulatin temperatures at the tp f the liner may be much ler than thse at the bttm f the liner. Thus, in designing the cement slurry 1

2 knledge f the actual temperature t hich it is expsed is an imprtant factr. In deep ells the actual dnhle temperature during cement setting may significantly differ frm the frmatin temperature. It shuld be als taken int accunt that a time lapse exists beteen the end f mud circulatin and placement f the cement.. BOTTOMOLE CIRCULATING TEMPERATURE.1. An empirical equatin It as fund that the bttmhle circulating temperature (T mb ) can be apprximated ith sufficient accuracy as a functin f t independent variables: the gethermal gradient (Γ) and the bttmhle static (undisturbed) temperature (T fb ). Assuming that fr deep ells T mb is a linear functin f T fb, e fund that the flling empirical expressin can be used fr predicting bttmhle circulating temperature T mb d d T. d d (1) fb Fr 79 field measurements (Kutasv and Targhi, 1987; Kutasv, 1999), a multiple regressin analysis cmputer prgram as used t btain the cefficients f the frmula. These cefficients are btained fr d 1 = C (-10.1 F), d = m (3354 ft), d 3 = 1.34, d 4 = 1. m/ C (.8 ft/ F) C (166 F) T fb 1. C (414 F), 1.51 C/100m (0.83 F/100ft) Γ 4.45 C/100m (.44 F/100ft). Therefre, the Eq. (1) shuld be used ith cautin fr extraplated values f T fb and Γ. The accuracy f the results (Eq. (1)) is 4.6 C, and as estimated frm the sum f squared residuals.. The equivalent API Wellbre methd American Petrleum Institute (API), Sub-cmmittee 10 (Well Cements) has develped ne temperature crrelatins fr estimating circulating temperatures fr cementing (Cvan and Sabins, 1995). T use the current API bttm-hle temperature circulatin (BCT) crrelatins (schedules) fr designing the thickening time f cement slurries (fr a given depth) the knledge f the averaged static temperature gradient is required. The surface frmatin temperature (SFT) fr the current API test schedules is assumed t be 80 F. Thus t calculate the static temperature gradient the static (undisturbed) temperature prfile f frmatins shuld be determined ith a reasnable accuracy. The value f SFT (the undisturbed frmatin temperature at the depth f apprximately f 50 ft, here the temperature is practically cnstant) f abut 80 F is typical nly fr ells in Suthern U.S. and sme ther regins. Fr this reasn the API test schedules cannt be used fr determinatin values f BCT fr cementing in ells drilled in deep aters, in areas remte frm the trpics, r in Arctic regins. Fr example, the equivalent parameter f SFT fr ffshre ells is the temperature f sea bttm sediments (mud line) that is clse t 40 F. In Arctic areas the value f SFT is ell bel the freezing pint f ater. Many drilling peratrs came t a cnclusin that cmputer temperature simulatin mdels (instead f the API schedules) shuld be used t estimate the cementing temperatures (nre et. al, 1993; Guillt et. al, 1993; Calvert and Griffin, 1998). It is lgical t assume that fr ells ith T 0 = 80 F a gd agreement beteen measured and estimated frm API crrelatins values f BCT shuld be expected. Therefre e suggested t transfrm a real ellbre t an Equivalent API Wellbre (Kutasv, 00). As an example let us cnsider a ell ith flling parameters: = 0,000 ft, Γ = 0.00 F /ft and T 0 = 60 F. Then the depth f the 80 F istherm is: (80-60)/0.00 = 1,000 (ft). Thus the vertical depth f the Equivalent API Wellbre is Similarly, fr a ell ith T 0 = 100 F, = 0,000-1,000 = 19,000 (ft). = 0, ,000 = 1,000 (ft). Bel e present simple equatins fr estimatin f the equivalent vertical depth (). Fr n land ell, Fr an ffshre ell, T0 80. () T 80 0, (3)

3 here T 0 is the temperature f bttm sediments (mud line) and Γ is the average temperature gradient in the sectin f the ellbre..3 Examples Tfb T0. (4) Bel e present t examples f determinatin bttm-hle circulating temperatures (BCT) by the API-EW Methd. Example 1 n land ell A (Figure ). The surface temperature T 0 = 50 F, vertical depth = 0,000 ft, and the static temperature gradient Γ = F/ft, and the bttm-hle static temperature is 350 F. Frm Eq. (3) e btain Figure : Temperature prfiles: A n land ell, B ffshre ell = 0,000 + (50-80)/0.015 = 18,000 (ft). Using the ne API BCT crrelatins (Cvan and Sabins, 1995) fr = 18,000 ft and Γ = F/ft e estimate that BCT = 91 F and this is in a fairly gd agreement ith value f 301 F determined frm Eq. () (nte that the averaged accuracy f the Eq. (1) is 8. F). Example ffshre ell B (Figure ). The ater surface temperature is 50 F, the temperature f bttm sediments a T 0 = 35 F, = 0,000 ft, Γ = F/ft, ater depth =,000 ft, and the bttm-hle static temperature is 305 F. Frm Eq. () e btain ,000,000 15,000ft. Frm ne API crrelatins (Cvan and Sabins, 1995) fr = 15,000 ft and Γ = F/ft e determined that BCT = 44 F and this is in a satisfactry agreement ith value f 56 F determined frm Eq. (1). 3. TE SUT-IN TEMPERATURE By using the adjusted drilling mud circulatin time cncept e btained an equatin fr dimensinless shut-in temperature (Kutasv, 1999). T s t Ts s - Tf T s, (5) T - T c f Ei 1 t / ts ats 1, t, (6) Ei s - r t at r c 1,, t Gt, (7) 4t here T s is the shut-in temperature, t s is the shut-in time, T c is the drilling fluid circulatin temperature (at a given depth), t c is drilling fluid circulatin time, T f is the frmatin (undisturbed) temperature. 3

4 The values f the functin G can be calculated frm Eqs. (7) and (8): 1 G 1, 1 AF F t 10,, (7) ln t exp 0.36 t G, t 10. (8) ln tc 1 n ln1 t, n /3, A 7/8 The crrelatin cefficient G(t ) varies in the narr limits: G(0) = and G( ) = FIEL EXAMPLE Well #4 (Venezuela) is a vertical ellbre. The ttal depth as 1,900 ft the bttmhle static temperature at 1,600 ft as 44 F. The casing size f this ell is 5 1/ in. And the hle size as 8 1/-in.=0.354 ft the 14.0 ppg cmpsite blend cement slurry as used (illenbeck et al., 00). We assumed that the surrunding frmatin is il-bearing sandstne ith thermal cnductivity 1.46 kcal/(m hr C) and thermal diffusivity m /hr. Let us assume that a prductin liner as set at a depth f 10,000 t 1,600 ft. A perid f 30 days as needed t drill this interval. In additin t this, 36 hurs ere needed t clean up the ell and pump the cement slurry; therefre, the duratin f the thermal disturbance f the frmatin at depth f 10,000 ft as 756 hrs ( ) days and at depth f 1,600 ft as 36 hurs. Let us assume that the gethermal gradient Γ = F/ft. Then the frmatin temperature is T f F 80 F F/ ft. The drilling mud circulating temperatures ere estimated frm Eq. (1): fr = 1,600 ft, T mb = 199 F, and fr = 10,000 ft, T mb = 16.5 F. The results f calculatins after Eq. (5) are presented in Figure 3 and Table 1. Figure 3: Shut-in temperatures fr t depths The temperature variatin (Table 1 and Figure 1) depends n the time f the cement slurry placement and can have a significant effect n the perfrmance f a cement system and has t be taken int accunt. Fr example, the temperature at depth f 10,000 ft after 6 hurs is nt 16.5 F (circulatin temperature), but F. Als, the temperature at the depth 1,600 ft after 6 hurs f shut-in is nt 199 F (circulatin temperature), but 18.1 F. The difference f 1-19 F can have a substantial impact n the cement slurry design. Fr bth depths the difference f T f T s after 6 hurs f shut-in is 5.9 and 35.5 F (Table 1). 4

5 Table 1: The difference T f T s fr t depths and values f γ t s, hrs T f T s, F h = 1,600 ft t c = 36 hrs T f = 44 F T c = 199 F γ T f T s, F h = 10,000 ft t c = 756 hrs T f = 10 F T c = 16.5 F Γ REFERENCES illenbeck, R.L., einld, T., Rgers, M.J., and Mmburquette, I.G.: The Effect f Cement heat ydratin n the Maximum Annular Temperature f Oil and Gas Wells, Prceedings, SPE presented at the SPE Ann. Techn. Cnf., 9 September - Octber 00, San Antni, Texas (00). Calvert,.G., and Griffin, T.J., Jr.: eterminatin f Temperatures fr Cementing in Wells rilled in eep Water, Prceedings, SPE paper presented at the 1998 IAC/SPE rilling Cnf., 3-6 March 1998, allas, Texas, (1998). Cvan, M., and Sabins, F.: Ne crrelatins imprve temperature predictins fr cementing and squeezing, Oil and Gas Jur., Aug. 1, (1995), p. 53. Eppelbaum, L.V., and Kutasv, I.M.: Temperature and pressure dradn ell testing: Similarities and differences, Jur. f Gephysics and Engineering, 3, N. 1, (006), 1-0. Guillt, F., Bisnault, J.M., and ujeux, J.C.:, A Cementing Temperature Simulatr t Imprve Field Practice, Prceedings, SPE paper 5696 presented at the 1993 SPE/IAC rilling Cnf., 3-5 February, Amsterdam (1993). nre, R.S., Jr., Tarr, B.A, ard, J.A., and Lang, N.K.: Cementing Temperature Predictins Based n Bth nhle Measurements and Cmputer Predictins: a Case istry, Prceedings, SPE paper 5436 presented at the Prductin Operatins Symp., 1-3 March, Oklahma City, OK, USA (1993). Kutasv, I.M.: Applied Gethermics fr Petrleum Engineers, Elsevier (1999). Kutasv, I.M.: Methd Crrects API Bttm-hle Circulating-Temperature Crrelatin, Oil and Gas Jur., July 15, (00), Kutasv, I.M., and Targhi, A.K.: Better eep-le BCT Estimatins Pssible, Oil and Gas Jur., 5 May, (1987), Rmer, J., and Lizz, M.: The Imprtance f ydratin eat n Cement Strength evelpment fr eep Water Wells, Prceedings, SPE paper 6894 presented at the 000 SPE Ann. Techn. Cnf. and Exhib., 1-4 Octber 000. allas, Texas, (000). 5