Unit 2 Drilling a well

1. Before reading the text, study the vocabulary.

tar sands	Гудронный песок, песчаник
crooked well	искривленная скважина
to exhaust	Изнашивать
self-defeating	Обреченный на провал
equation	Уравнение
rotation time	Время обращения
wildcat	Разведочная скважина
offset wells	Соседние, периферийные скважины
electric logs	Диаграмма электрического каротажа; Диаграмма результатов геофизических исследований в скважине
mud recaps	Характеристики бурового раствора
to spud in	Начинать бурение скважины
vendors	Поставщики
toolpusher, drilling foreman	Буровой мастер

2. Practise the pronunciation of the following words:

   • variety

   • variable

   • South Louisiana

   • West Texas

   • purpose

   • ultimate indicator

   • business endeavor

   • equation

3. Read and translate the text.

Drilling an oilwell, or making hole, as it is referred to by those in the oil industry, is a complex business. Drilling for oil involves as much art as science. For a particular well, even experienced drillers may have differences of opinion on the right way to make hole. Some oilmen will tell you that there is just one rule to follow in drilling: set the bit on the bot­tom and turn it to the right. That's no doubt cor­rect, but a lot of things have to be determined before that bit goes to work. What type of bit should be used? How much weight should be imposed on the bit? What characteristics should the mud have? These are just a few of the critical questions that must continually be answered as a well is drilled.

Explaining the fine points of oil field geology, engineering, technology, and economics in a way that applies to every well is almost impossible, because of the great variety of drilling situations throughout the world. Well specifications vary from one oil field to the next. A successful drilling program for a well in South Louisiana, for instance, would be a waste of time for a driller in Oklahoma hard-rock country. And what may work in California's shallow tar sands is drastically different from the demands of ultra-deep, high-pressure gas wells in West Texas. But whatever the drilling conditions, every drilling contractor has the same purpose in mind: to drill a usable well to the operator's specifications for the lowest possi­ble cost. Usually, that means accom­plishing those objectives in the shortest time possible because in drilling, time is money.

Cost per foot is the ultimate indicator of drill­ing success. A hole that is drilled fast and crooked or that creates cementing problems later on is not much of a cost saver. On the other hand, a picture-perfect well project that exhausts a large number of bits or takes so long to drill that rig costs become prohibitively high is self-defeating as a business endeavor. The following equation can be used as a basis for drilling cost calculations:

		B + Cr (t+T)
Cf	=
		F

Where

Cf	- cost per foot drilled;
B	- bit cost;
Cr	- rig cost in dollars per hour;
t	- rotation time;
T	- tripping time;
F	- footage per bit;

Rig costs and bit costs vary from well to well, but in every case, correct drilling practices can make each bit drill further, reducing tripping time and keeping the total well cost down. A good driller is concerned with the six basic fac­tors that affect the rate of penetration (ROP):

1. the type of bit used;

2. weight on bit;

3. rotary speed;

4. drilling fluid properties;

5. hydraulics; and

6. formation properties.

The successful drilling program will be the most efficient combination of variable factors for the formation being drilled. Effective least-cost drilling, or optimization, begins with good well planning. Every well is not a wildcat. Other wells in the area of interest, known as offset wells, can be a good source of information for a drilling project. A review of the separate costs of such wells, using geologic maps, bit records, electric logs, daily drilling reports, and mud recaps can give the drilling contractor a pretty good idea of what to expect before the well is spudded in.

At some time before the drilling actually begins, a pre-spud meeting is held, during which representatives of the operating company and the drilling company review the terms of the contract for the benefit of those who are to be directly involved in drilling the well. Among the items of discussion are the preparation of the location, the water source, any vendors or ser­vices to be contracted, reporting of well data, the well program, the mud program, and any special provisions that may be included in the contract. In short, the pre-spud meeting estab­lishes a plan of action for drilling the well and suggests how certain problems are to be dealt with if they arise.

Since it is impossible to predict everything that may occur in drilling, many decisions must be left to the toolpusher and the drilling foreman after drilling is underway. The per­formance of the drilling crew and service com­panies, execution of the well program, and maintenance of all rig equipment are among the responsibilities of drilling personnel.