A well coring apparatus (10) includes an outer barrel (12) and an inner barrel (18). The inner barrel (18) is sealed with a rupturable diaphragm (24) and a check valve (49). A sponge (50) is disposed around the inner walls of the inner barrel (18) for contacting the core (58). A fluid (54) is disposed in the sealed inner barrel (18) to prewet the sponge (50). A piercer (32) is reciprocally disposed within the outer barrel (12) and has a conical shaped surface (38), the apex of which is operable to pierce the diaphragm (24). In response to forming of the core (58), the fluid (54) displaced by the core (58) prevents drilling mud from being disposed between the core (58) and the sponge (50).
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