3. Field Appraisal

If an exploratory well shows that hydrocarbons are present, more seismic data is gathered and then a number of appraisal wells are drilled and more data is collected. From th__ __¹⁾ data i__²⁾ is poss__ __ __ __³⁾ to esti__ __ __ __⁴⁾ how mu__ __⁵⁾ oil a__ __⁶⁾ gas t__ __⁷⁾ field cont__ __ __ __⁸⁾, how diff__ __ __ __ __⁹⁾ it wi__ __¹⁰⁾ be t__¹¹⁾ extract a__ __¹²⁾ what perce__ __ __ __ __¹³⁾ of t__ __¹⁴⁾ oil a__ __¹⁵⁾ gas c__ __¹⁶⁾ be extr__ __ __ __ __¹⁷⁾. Unfortunately, i__¹⁸⁾’s n__ __¹⁹⁾ possible t__²⁰⁾ get ev__ __ __²¹⁾ last dr__ __²²⁾ of o__ __²³⁾ out o__²⁴⁾ a reservoir - i__²⁵⁾ the No__ __ __²⁶⁾ Sea, f__ __²⁷⁾ example, oper__ __ __ __ __²⁸⁾ expect t__²⁹⁾ recover ab__ __ __³⁰⁾ 40 - 50% of t__ __³¹⁾ total rese__ __ __ __ __³²⁾. This fig__ __ __³³⁾ may se__ __³⁴⁾ quite l__ __³⁵⁾, but reme__ __ __ __³⁶⁾ there i__ __³⁷⁾’t a la__ __³⁸⁾ of o__ __³⁹⁾ and g__ __⁴⁰⁾. Instead i__⁴¹⁾ is tra__ __ __ __⁴²⁾ in t__ __⁴³⁾ pores o__⁴⁴⁾ the rese__ __ __ __ __⁴⁵⁾ rock a__ __⁴⁶⁾ you c__ __⁴⁷⁾ appreciate th__ __⁴⁸⁾ it i__ __⁴⁹⁾’t poss__ __ __ __⁵⁰⁾ to g__ __⁵¹⁾ every la__ __⁵²⁾ drop o__ __⁵³⁾. Think ba__ __⁵⁴⁾ to t__ __⁵⁵⁾ idea th__ __⁵⁶⁾ oil i__⁵⁷⁾ held i__⁵⁸⁾ pores i__⁵⁹⁾ much t__ __⁶⁰⁾ same w__ __⁶¹⁾ that wa__ __ __⁶²⁾ is he__ __⁶³⁾ in a spo__ __ __⁶⁴⁾. We kn__ __⁶⁵⁾ that i__⁶⁶⁾ isn’__⁶⁷⁾ possible t__⁶⁸⁾ get ev__ __ __⁶⁹⁾ last lit__ __ __⁷⁰⁾ drop o__⁷¹⁾ water o__ __⁷²⁾ of a spo__ __ __⁷³⁾ - it’__⁷⁴⁾ always a b__ __⁷⁵⁾ damp. O__ __⁷⁶⁾ exploration invo__ __ __ __⁷⁷⁾ lots o__⁷⁸⁾ people wi__ __⁷⁹⁾ different ski__ __ __⁸⁰⁾, for exa__ __ __ __⁸¹⁾ geologists, geophy__ __ __ __ __ __ __⁸²⁾, surveyors, mudlo__ __ __ __ __⁸³⁾, computer scien__ __ __ __ __⁸⁴⁾, marine biolo__ __ __ __ __⁸⁵⁾, drilling engi__ __ __ __ __⁸⁶⁾, the dril__ __ __ __⁸⁷⁾ crew. Alongside these are all the people employed back onshore for example economists, planners, lawyers, IT specialists, environmental advisers and safety advisors to name a few.

4. Miscible methods

One method of enhanced recovery is based on the injection of natural gas either at high enough pressure or containing enough petroleum gases in the vapour phase to make the gas and oil miscible. This met__ __ __¹⁾ leaves lit__ __ __²⁾ or n__³⁾ oil beh__ __ __⁴⁾ the dri__ __ __ __⁵⁾ gas, b__ __⁶⁾ the relat__ __ __ __ __⁷⁾ low visc__ __ __ __ __⁸⁾ of t__ __⁹⁾ gas c__ __¹⁰⁾ lead t__¹¹⁾ the bypa__ __ __ __ __¹²⁾ of la__ __ __¹³⁾ areas o__¹⁴⁾ oil, espec__ __ __ __ __¹⁵⁾ in reser__ __ __ __ __¹⁶⁾ that a__ __¹⁷⁾ not homog__ __ __ __ __ __¹⁸⁾. Another enha__ __ __ __¹⁹⁾ method i__²⁰⁾ intended t__²¹⁾ recover o__ __²²⁾ that i__²³⁾ left beh__ __ __²⁴⁾ by a water__ __ __ __ __²⁵⁾ by put__ __ __ __²⁶⁾ a band o__²⁷⁾ soaplike surfa__ __ __ __ __²⁸⁾ material ah__ __ __²⁹⁾ of t__ __³⁰⁾ water. T__ __³¹⁾ surfactant cre__ __ __ __³²⁾ a very l__ __³³⁾ surface ten__ __ __ __³⁴⁾ between t__ __³⁵⁾ injected mate__ __ __ __³⁶⁾ and t__ __³⁷⁾ reservoir o__ __³⁸⁾, thus allo__ __ __ __³⁹⁾ the ro__ __⁴⁰⁾ to b__⁴¹⁾ ”scrubbed” cl__ __ __⁴²⁾. Often t__ __⁴³⁾ water beh__ __ __⁴⁴⁾ the surfa__ __ __ __ __⁴⁵⁾ is ma__ __⁴⁶⁾ viscous b__⁴⁷⁾ addition o__⁴⁸⁾ a polymer i__⁴⁹⁾ order t__⁵⁰⁾ prevent t__ __⁵¹⁾ water fr__ __⁵²⁾ breaking thr__ __ __ __⁵³⁾ and bypa__ __ __ __ __⁵⁴⁾ the surfa__ __ __ __ __⁵⁵⁾. Surfactant floo__ __ __ __⁵⁶⁾ generally wo__ __ __⁵⁷⁾ well i__⁵⁸⁾ noncarbonate ro__ __⁵⁹⁾, but t__ __⁶⁰⁾ surfactant mate__ __ __ __⁶¹⁾ is expe__ __ __ __ __⁶²⁾ and la__ __ __⁶³⁾ quantities a__ __⁶⁴⁾ required. O__ __⁶⁵⁾ method th__ __⁶⁶⁾ does se__ __⁶⁷⁾ to wo__ __⁶⁸⁾ in carb__ __ __ __ __⁶⁹⁾ rock i__⁷⁰⁾ the inje__ __ __ __ __⁷¹⁾ of car__ __ __⁷²⁾ dioxide, eit__ __ __⁷³⁾ alone o__⁷⁴⁾ in conju__ __ __ __ __ __⁷⁵⁾ with nat__ __ __ __⁷⁶⁾ gas. T__ __⁷⁷⁾ carbon dio__ __ __ __⁷⁸⁾ can gre__ __ __ __⁷⁹⁾ improve reco__ __ __ __⁸⁰⁾, but ve__ __⁸¹⁾ large quant__ __ __ __ __⁸²⁾ at a reaso__ __ __ __ __⁸³⁾ price a__ __⁸⁴⁾ necessary. Most of the successful projects of this type depend on tapping and transporting (by pipeline) carbon dioxide from underground reservoirs.