Drilling mud resistivity and mud filtrate resistivity were measured, using the synthetic muds: those are clay base muds with additives (salt•humic acids•CMC•barite) and oil emulsion muds with additives.
From the standpoint of electric log interpretation, dependence of these resistivities on temperature (15°C_??_80°C) and different mud additives is discussed, and the relationship between mud resistivity and mud filtrate resistivity investigated.

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Purpose of this paper is to present laboratory data to aid in the evaluation of a damage of drilling fluids to oil sands. In this study were used onsolidated synthetic cores mixing river sand with cement. Permeabilities of these samples were between 7 and 3000 md. Firstly, the effective oil permeability of a core was measured. Secondly, the core was mounted on the assembly shown in Fig. 1 and mud fluid was invaded into the core under pressure of 5 kg/cm² for three hours. Thirdly, oil was forced to flow upward under certain pressure, and effective oil permeability was measured again. Thus, the recovery in effective oil permeability was obtained and the damage of drilling fluids to oil sands was evaluated. The results of these tests are shown in Figs. 2_??_5.
Fig. 2 indicates that in bentonite mud the permeability recovery was very low, especially in low oil pressure. If mud cake was removed, the recovery increased to some degree. Fig. 3 indicates that in oil emulsion mud the permeability recovery was also low. Figs. 4 and 5 indicate that the permeability recovery in oil-base mud was higher than that of water-base mud. The recovery, however, was not sufficiently high except for samples without mud cake.

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We use “chrome muds” in many wells in our company since last year.
Chrome muds are mainly composed of bentonite, ferro-chrom lignosulfonate, chromenite (our patented material), caustic soda, etc..
Chrome muds have many excellent advantages compared with Ca-system muds or other special muds.
Some of them are as follows:
(1) easy preparation and maintenance
(2) high stability
(3) good inhibition for swelling of shale
(4) low water loss
(5) low cost
In this paper we explain an outline of composition, preparation, maintenance and field results.

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The authors investigated on capillary pressure, relative permeability and resistivity using unconsolidated sands which were water-wet or oil-wet. The preferentially water-wet sands were treated so as to make the surface to be preferentially oil-wet. The results are discussed in terms of the effect
of changes in wettability on some properties in the petroleum reservoir engineering.

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