Infill Drilling Project
Aldrich Anticline
T17S-R25W
Ness County, Kansas

Background:  The Aldrich Anticline infill drill project was funded by a 1999 grant to Pangaea Geochemical Technologies from the Kansas Technology Enterprise Corporation. Pangaea offered K-Series gas-sieve, light hydrocarbon soil vapor surveys in the Red Top Program.  Participating independent oil operators provided survey locations for Pangaea's gas-sieve surveys and in exchange Pangaea provided the operators survey data at no charge.  The survey area were already slated for the drilling of at least one test well in 1999 or early 2000.  In most cases the drilling locations were already chosen when the geochemical survey was conducted.  The results of the surveys were provided to the operators prior to drilling activity.  The data from the program was used to develop interpretation models for gas-sieve geochemical surveys.

Geology:  The Aldrich Anticline project was chosen because it occurs in a highly prolific, multi-pay, mature exploration play. The operator intended to drill two infill locations in the Fall of 1999 on the Aldrich Anticline Structure where two zones, the Fort Scott limestone and the Mississippi dolomite were thought to be in a good structural position with excellent zone development.  The Ft. Scott is the upper pay zone and has been produced through primary production only.  Generally, this zone is considered to be a good future candidate for water flooding. The lower zone is the highly prolific Mississippi dolomite that is a, at least in part, water drive.

Gas-sieve survey:  A 22-point gas-sieve survey was conducted prior to the operators 1999 drilling program. The sampling grid is on 10 acre spacing because that is the spacing that the operators plans to drill infill wells.  The results of the gas-sieve survey are depicted on Map 1. Note that this is a total hydrocarbon map (ethane + propane + butane concentrations in ug/L).  Methane was not considered in the data set because the data is noisy due to an unknown quantity of bacterially produced methane.  Map 2 is a map of the ratio of ethane concentration/propane concentration.  This data is unitless and only shows where the hydrocarbons, emanating from the reservoir below, have similar compositions. 

Data point N-6 was the location for the first well to be drilled.  Data point N-19 was the location of the second well to be drilled.  Both locations appeared to be excellent location based on Fort Scott and Mississippi structural maps and the operator considered them to be equally prospective.

Results:  Proposed location #1 drilled to be structurally high on the Ft. Scott and the Mississippi with good zone development in the Mississippi and the thickest Ft. Scott zone in the field. Ft. Scott DST's showed some pressure loss over virgin pressure because of decades of fluid withdrawal from this gas solution drive zone. The well was completed for 45 BOPD with no decline to date.

Proposed location #2 was drilled and encountered a high structural position on both the Ft. Scott and the Mississippi.  There was poor zone development in both zones.  The operator attempted to enhance recoveries by first acidizing this well followed by an acid frac. The well responded poorly and has stabilized at 9 barrels of total fluid a day with 3 BOPD.

Analysis of geochemistry data:  Interestingly, the total hydrocarbon data at point N-19 suggested that this was an inferior well location.  Additionally, the ethane/propane ratio map suggested that the small quantity of light hydrocarbon that is gassing off from these portions of the anticline does not have the same composition as the soil gas over the productive parts of the anticline.  The interpretation is that the ratio map shows were the anticline is of reservoir quality and the total hydrocarbon map shows where there is still producible oil.  Other, similar projects, performed in the Red Top program contribute to the validity of the interpretation.

Note that a ratio of 1.7 is not a “magic number”.  The composition of the gases emanating from various reservoir in various geologic basins have their own magic composition numbers that are obvious in most gas-sieve data sets.

Used together, the two geochemistry maps suggest that location N-1, N-2, N-10, N-7, and N-16 have good potential as infill drill locations having both higher total hydrocarbons and a ratio of 1.7 or greater.  N-2 is the best location among this group.

Locations N-18, N-8, and N-3 have lower total hydrocarbon values but, they have ratios suggesting they are situated in reservoir quality rocks. Together, this indicates that these locations have been drained by other nearby wells. They could become important locations for water flood management.

Other locations such as N-9, N-4, N-5, N-14, N-15 have neither good hydrocarbons nor good ratio values suggesting that they are very poor candidates for future drilling locations.