A differentiation is made between two types of loss in head. The first results from the alteration in the transmissibility of the permeable formation in the immediate vicinity of the well bore. This alteration is caused by the process of drilling and completing the well. The skin factor is a measure of resultant head loss, and methods for evaluating this well parameter are discussed. The second type of well loss is caused by turbulent flow in the formation close to the well, and is commonly evaluated by a step-drawdown test. The interpretation of such tests is investigated, and a method of analysis is proposed which is believed to have a theoretically sounder basis than that commonly employed.

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