Abstract
Results of a study on the invasion of mud fluid into free gas zone tested by the use of artificial consolidated sands are described in this paper. Some of the results obtained are as follows: (1) as mud pressure increases the speed of invasion increases, (2) barite mixed in mud fluid affects a little on the speed of invasion, (3) CMC in mud fluid decreases the speed of invasion, and (4) as the degree of reduction of gas permeability of sands by mud invasion, it is conspicuously smaller on the cores of originally lower permeability and on the cores of which mud invaded longer time.
