General Field Information |
| Produces Oil: Yes Produces Gas: Yes |
| Geologic Province: |
Central Kansas Uplift (Pratt Anticline) |
| Exploration Method: |
Subsurface mapping |
| Surface Formation: |
Nippewalla |
| Oldest Formation Penetrated: |
Arbuckle |
| Drilling Casing Practices: |
Kan-Ex used standard rotary drilling with a chemical mud system. When chloride levels became too high, the mud system was displaced on some wells. Lost circulation is a potential hazard, as one operator twisted off loosing drill collars and some drill pipe. Therefore, it is common practice to drill hole ahead to 1000' and then go back and set the minimum surface pipe if no lost circulation is encountered.
Kan-Ex DST'd the Mississippi Chert Conglomerate in all wells. A single core was cut in the #2 Onstot. All Kan-Ex wells were completed by cementing 5 1/2" casing through the Mississippi Conglomerate zone and perforating; in most cases with a tubing conveyed gun. Production was natural where possible. Subsequently most wells required 500 to 1500 G 7 ½% INS Acid, and eventually almost all wells were fac'd with CO-2 or gelled KCL water. (9,000 to 20,000# sand). |
| Electric Logging Practices: |
All producing Kan-Ex wells were logged by Gearhart, using a Compensated Neutron-Density and a Dual Induction Laterlog. Also, all producing Kan-Ex wells have a Cement Bond Log. |
| Comments: |
Continued from the Discussion: A possible scenario for the deposition of the Kan-Opener would first require uplift of the Chitwood field area (one mile north of the Kan-Opener), associated with the post-Osagian sea regression. This would be followed by extensive weathering of now subaerial exposed Osagian Chert. Next the author visualizes the deposition of an alluvial fan type sieve deposit, Bull (1972, pp. 68-69)*, composed of weathered Osage Chert traveling down the side of this dome shaped structure and into the present area of the Kan-Opener Field. Subsequently, this extensively weathered cobble-boulder conglomerate was inundated by a "sudden" influx of mud (mud flow?), which was forced, while in a plastic state, downward between the rock fragments (in some places small inclusions in the shale matrix appear to form flow lines in between rock fragments, showing the direction of flowage). Difficult to explain are the fractured and broken rock fragments that appear to have been shattered in situ and then expanded into an "exploded view" set in the seemingly once plastic green shale matrix.
Deposited over this conglomerate is a 1' to 2' grey-black carbonaceous fissle shale that was then overlain by a 1' to 3' thick arenaceous calcareously cemented, cherty pebble conglomerate.
Subsequently vertical fracturing, under considerable pressure, resulted in the formation of slickensides along some fracture faces, and in increased permeability, although many fractures are healed with sparry calcite cement.
The main difference between the upper and lower conglomerate zones, besides the obvious large difference in grain size, is the porosity type. The upper zone porosity and permeability is almost 100% attributable to interparticle porosity,while in contrast, the lower thicker main reservoir's porosity and permeability is nearly 100% attributable to intraparticle porosity.
From a hydrocarbon recovery standpoint, since the Kan-Opener Field is stratigraphically trapped and contains no water, the sole reservoir drive mechanism is the expanding gas cap of this over saturated reservoir. As a result of gas production, it now appears primary oil recovery may be less than 15% of the calculated volumetric reserves in the Kan-Opener Field. Therefore, if and when future reservoirs of this nature are discovered, operators should be aware that it is essential to begin a pressure maintenance program immediately in order to maximize the primary oil recovery.
As we continue our exploration efforts in this "ultra-mature basin" we should keep in mind the erudite observations of Dickey (1958): "We usually find oil in new places with old ideas. Sometimes, also, we find oil in an old place with a new idea, but we seldom find much oil in an old place with an old idea. Several times in the past we have thought that we were running out of oil, whereas actually we were only running out of ideas".
---------- Footnote ----------
*(as described by Bull, a "sieve deposit" is a lobate gravel deposit that is found near a fractured source area that supplies very little sand, silt or clay to the fan. The deposit may be sufficiently permeable to allow water from a flood discharge to infiltrate completely before reaching the toe of the fan, thus, the water is permitted to pass through the fan rather than over, while the coarse material in transport is held back, thus resulting in a strainer (sieve) effect. |
| Discussion: |
As of 1985, the Kan-Opener Field appeared to be a geologic oddity. Prior to that time, production from the Mississippian/(Basal Pennsylvanian) Conglomerate in this area had been rare and almost always non-commercial.
On the basis of electric logs, many of the dry holes in the area have a chert section that is equally "clean" and porous to the producing wells, yet tested low bottom hole pressures and very restricted permeability. In constructing a cross-plot graph of shale corrected porosity vs. resistivity, (Asquith, 1982, p. 120), it appears that dry holes and producing wells commonly plot together, therefore, this method of no value in determining wells from dry holes.
Because some producing wells in the Kan-Opener Field have a greater shale content than others, a simple isopach map oversimplifies the reservoir geometry. Therefore, an "effective porosity volume" map was constructed. This was accomplished by first correcting the averaged neutron-density porosity for shale volume, and then finding the summation of "porosity-feet" for each well. This "effective porosity feet" number was plotted by the well with the overall formation thickness, along with their ratio: effective porosity feet / height feet = average porosity), and the porosity range (minimum to maximum). Contouring the "effective porosity feet" values graphically displays the areal extent and "quality" of the reservoir, (in effect where the oil and gas is contained volumetrically). The two best wells in the field have the largest "effective porosity feet" values and two of the poorer wells have the smallest values. The Hummon dry hole in the NW SW of Section 3, which tested 200# BHP, doesn't fit the model, however, the entire Conglomerate zone was not covered by the DST.
One might anticipate a thinning of the Marmaton directly over the field, but, an isopach of the over-lying Marmaton Group shows a thickening to the west and a thinning to the east. This difference, in assumed paleoelevation, could have provided the hydrastic "head" necessary to drive meteoric waters through this part of the formation to further develop the secondary porosity. The shale content variation to the west, south and southeast, however, must be explained depositionally, not diagenetically.
Depositionally a complex series of geologic events was necessary to result in the formation of the Kan-Opener Field.
(Discussion is continued in the Comments field). |
|
| Geological Age: |
Post-Osagian to Pre-Desmoinesian |
| Depositional Environment: |
The environment of deposition for this clastic reservoir is uncertain, however, a few very sparse invertebrate marine fossils have been found in the green shale matrix, pointing towards a marine deposition of the shale. |
| Formation Lithology: |
Formation: Chert Conglomerate (Upper Porosity Streak)
Present in almost all producing wells is a 1' to 3' "higher" porosity streak at the top of the conglomerate zone. This "porosity streak" is usually separated from the rest of the conglomerate by a black fissle shale. This upper zone is a poorly sorted chert pebble conglomerate. The subrounded to angular 1/4" to 1" chert rock fragment is set in a fine grained calcareously cemented sandstone matrix. There is some indication of crossbedding. This zone has an excellent intergranular porosity in most wells.
Formation: Chert Conglomerate (Main Producing Zone)
The main producing zone is a poorly sorted pebble to boulder conglomerate composed primarily of brown oil saturated tripolitic chert "floating" in a green shale matrix. Most rock fragments have been in situ brecciated. There are some apparent flow structures where the green shale matrix "flowed" around the brecciated rock fragments. Some secondary fracturing has slickensides. Many chert cobbles have an excellent fossil moldic porosity. Fossil molds and fractures are commonly lined with a black asphaltic residue. Some larger chert cobbles are "zoned" with white weathered chert centers grading into a highly tripolitic brown oil stained outer "halo". |
| Formation Geometry: |
The reservoir is an ovoid-ellipse, elongate in a northeasterly direction. Dry holes on the west and south have high obvious shale contents and define the reservoir in these directions. The field boundary is less clear to the northeast and east where in dry holes it has similar shale content, thickness, porosity and resistivity, but a much reduced permeability. |
| Trap Type: |
Stratigraphic |
