5. Thermal methods

There are many reservoirs, usually shallow, that contain oil which is too viscous to produce well. Nevertheless, thr__ __ __ __¹⁾ the appli__ __ __ __ __ __²⁾ of he__ __³⁾, economical reco__ __ __ __⁴⁾ from th__ __ __⁵⁾ reservoirs i__⁶⁾ possible. He__ __ __⁷⁾ crude oi__ __⁸⁾, which m__ __⁹⁾ have a visc__ __ __ __ __¹⁰⁾ up t__¹¹⁾ one mil__ __ __ __¹²⁾ times th__ __¹³⁾ of wa__ __ __¹⁴⁾, will sh__ __¹⁵⁾ a reduction i__¹⁶⁾ viscosity b__¹⁷⁾ a factor o__¹⁸⁾ 10 for ea__ __¹⁹⁾ temperature incr__ __ __ __²⁰⁾ of 50° C (90° F). T__ __²¹⁾ most succe__ __ __ __ __²²⁾ way t__²³⁾ raise t__ __²⁴⁾ temperature o__²⁵⁾ a reservoir i__²⁶⁾ by t__ __²⁷⁾ injection o__²⁸⁾ steam. I__²⁹⁾ the mo__ __³⁰⁾ widespread met__ __ __³¹⁾, called st__ __ __³²⁾ cycling, a quan__ __ __ __³³⁾ of st__ __ __³⁴⁾ is inje__ __ __ __³⁵⁾ through a we__ __³⁶⁾ into a form__ __ __ __ __³⁷⁾ and all__ __ __ __³⁸⁾ time t__³⁹⁾ condense. Conden__ __ __ __ __ __⁴⁰⁾ in t__ __⁴¹⁾ reservoir rele__ __ __ __⁴²⁾ the he__ __⁴³⁾ of vapori__ __ __ __ __ __⁴⁴⁾ that w__ __⁴⁵⁾ required t__⁴⁶⁾ create t__ __⁴⁷⁾ steam. Th__ __⁴⁸⁾ the sa__ __⁴⁹⁾ well i__⁵⁰⁾ put o__⁵¹⁾ production. Af__ __ __⁵²⁾ some wa__ __ __⁵³⁾ production, hea__ __ __⁵⁴⁾ oil fl__ __ __⁵⁵⁾ into t__ __⁵⁶⁾ well bo__ __⁵⁷⁾ and i__⁵⁸⁾ lifted t__⁵⁹⁾ the sur__ __ __ __⁶⁰⁾. Often t__ __⁶¹⁾ cycle c__ __⁶²⁾ be repe__ __ __ __⁶³⁾ several ti__ __ __⁶⁴⁾ on t__ __⁶⁵⁾ same we__ __⁶⁶⁾. A less com__ __ __⁶⁷⁾ method invo__ __ __ __⁶⁸⁾ the inje__ __ __ __ __⁶⁹⁾ of st__ __ __⁷⁰⁾ from o__ __⁷¹⁾ group o__⁷²⁾ wells wh__ __ __⁷³⁾ oil i__⁷⁴⁾ continuously prod__ __ __ __⁷⁵⁾ from ot__ __ __⁷⁶⁾ wells.

A__⁷⁷⁾ alternate met__ __ __⁷⁸⁾ for hea__ __ __ __⁷⁹⁾ a reservoir invo__ __ __ __⁸⁰⁾ the combu__ __ __ __ __⁸¹⁾ of a pa__ __⁸²⁾ of t__ __⁸³⁾ reservoir o__ __⁸⁴⁾ and i__⁸⁵⁾ called i__⁸⁶⁾ situ combu__ __ __ __ __⁸⁷⁾. Large quant__ __ __ __ __⁸⁸⁾ of compr__ __ __ __ __⁸⁹⁾ air mu__ __⁹⁰⁾ be inje__ __ __ __⁹¹⁾ into t__ __⁹²⁾ oil zo__ __⁹³⁾ to sup__ __ __ __⁹⁴⁾ the combu__ __ __ __ __⁹⁵⁾. The opt__ __ __ __⁹⁶⁾ combustion tempe__ __ __ __ __ __⁹⁷⁾ is 500° C (930° F). T__ __⁹⁸⁾ hot combu__ __ __ __ __⁹⁹⁾ products mo__ __¹⁰⁰⁾ through t__ __¹⁰¹⁾ reservoir t__¹⁰²⁾ promote o__ __¹⁰³⁾ production. In situ combustion has not seen widespread use.

6. The turbodrill

One variation in rotary drilling employs a fluid-powered turbine at the bottom of the borehole to produce the rotary motion of the bit. Known a__¹⁾ the turbo__ __ __ __ __²⁾, this instr__ __ __ __ __³⁾ is ab__ __ __⁴⁾ nine met__ __ __⁵⁾ long a__ __⁶⁾ is ma__ __⁷⁾ up o__⁸⁾ four ma__ __ __⁹⁾ parts: t__ __¹⁰⁾ upper bea__ __ __ __¹¹⁾, the tur__ __ __ __¹²⁾, the lo__ __ __¹³⁾ bearing, a__ __¹⁴⁾ the dr__ __ __¹⁵⁾ bit. T__ __¹⁶⁾ upper bea__ __ __ __¹⁷⁾ is atta__ __ __ __¹⁸⁾ to t__ __¹⁹⁾ drill pi__ __²⁰⁾, which eit__ __ __²¹⁾ does n__ __²²⁾ rotate o__²³⁾ rotates a__²⁴⁾ a slow ra__ __²⁵⁾ (6 to 8 revol__ __ __ __ __ __²⁶⁾ per min__ __ __²⁷⁾). The dr__ __ __²⁸⁾ bit, mean__ __ __ __ __²⁹⁾, rotates a__³⁰⁾ a much fas__ __ __³¹⁾ rate (500 t__³²⁾ 1,000 revolutions p__ __³³⁾ minute) th__ __³⁴⁾ in conven__ __ __ __ __ __³⁵⁾ rotary dril__ __ __ __³⁶⁾. The po__ __ __³⁷⁾ source f__ __³⁸⁾ the turbo__ __ __ __ __³⁹⁾ is t__ __⁴⁰⁾ mud pu__ __⁴¹⁾, which for__ __ __⁴²⁾ mud thr__ __ __ __⁴³⁾ the dr__ __ __⁴⁴⁾ pipe t__⁴⁵⁾ the tur__ __ __ __⁴⁶⁾. The m__ __⁴⁷⁾ is dive__ __ __ __⁴⁸⁾ onto t__ __⁴⁹⁾ rotors o__⁵⁰⁾ the tur__ __ __ __⁵¹⁾, turning t__ __⁵²⁾ lower bea__ __ __ __⁵³⁾ and t__ __⁵⁴⁾ drill b__ __⁵⁵⁾. The m__ __⁵⁶⁾ then pas__ __ __⁵⁷⁾ through t__ __⁵⁸⁾ drill b__ __⁵⁹⁾ to sc__ __ __⁶⁰⁾ the ho__ __⁶¹⁾ and ca__ __ __⁶²⁾ chips t__⁶³⁾ the sur__ __ __ __⁶⁴⁾. The turbo__ __ __ __ __⁶⁵⁾ is cap__ __ __ __⁶⁶⁾ of ve__ __⁶⁷⁾ fast dril__ __ __ __⁶⁸⁾, but t__ __⁶⁹⁾ bit a__ __⁷⁰⁾ bearings we__ __⁷¹⁾ quickly i__⁷²⁾ the ha__ __ __⁷³⁾ environment. Turbodrills were widely used in the former Soviet republics of Russia and Central Asia, but they are rare elsewhere.