问答题 翻译：Land maps are essential in establishing control wells and provide fundamental orientation. As Fig.2 illustrates, land maps which are readily available within most companies as well as readily available commercially, provide offset operators, total depth, formation tops and development dates. The land map is essential in establishing orientation and control.

问答题 翻译：A major oil company usually initiates the sequence of events that leads to the drilling of oil and gas wells in foreign fields, but independent oil operators pay for most of the wells in the United States. In fact, about 80% of all wells drilled in the U.S. today are financed by independents.

问答题 翻译：Practically every rig uses internal-combustion engines as its prime power source, or its prime mover.