Bypassed Pay Course Outline
Mud only produced on test, so formation content unknown. This can be due to either:
too large a test interval or
too short a flow time to produce the sump mud or
a slow mud leak from annulus to test string prior to and during test.
Water produced from below test interval in straddle test (lower packer failure not recognized).
Simple "skin" damage.
Deep Damage (zone mistakenly identified as tight).
Filtrate invasion in zones - resulting in large volumes of "water" recovered mistaken as formation water.
Gas block in low kh oil zones or rocks with certain pore geometry ("s" curves).
Test tool off depth (fill is problem in conventional straddles).
Tool plugging obscuring zone content or reducing flow rate.
False depletion (wrongly abandoned).
Misruns not tested.
Misleading recoveries from DSTs with several tests carried out on a single trip in the hole (Multiple Resets).
"Tight Hole" tests run in the fifties/sixties for security, where the tight chamber volume was sized too small to recover anything but rat hole mud.
Incorrect positioning of tool perfs far below or above porosity, so only mud recovered.
Water cushions obscuring low rate gas in deep hot wells.
Imbibition and resulting water block in deep basin type reservoirs with large gas columns, identified as "filtrate flow back" signature on DSTs (first recognized by Murray Grigg).
Incorrect Reservoir Analysis. Erroneous interpretation of Horner Plots, eg. linear flow wrongly interpreted as depletion