ABSTRACT: Depositional Facies Distributions, Diagenetic, and Structural Controls on Producing Intervals, Pennsylvanian Spiro Formation, South Hartshorne Field, Latimer County, Oklahoma

DEMECS, STEVEN S., and PAUL K. MESCHER, ARCO Oil and Gas Co., Plano, TX, and MARK LONGDEN and MARK A. WARD, ARCO Oil and Gas Co., Midland, TX

The Spiro (Pennsylvanian-Lower Atokan) Formation of the Arkoma basin has long been a prolific dry gas reservoir in the southern Arkoma basin of Oklahoma. Integration of core and petrographic studies with structural mapping from ARCO and partnership wells in the South Hartshorne field area reveals a complex pattern of depositional facies, diagenetic alterations, and structural position control porosity distributions in the Spiro Formation. Depositional facies consist of complex mixed siliciclastic and carbonate depositional systems consisting of shallow shelfal, high-energy barrier system sediments. Primary interparticle porosity and secondary fracture porosity are the main producing pore types. Carbonate sections are dominated by high-energy, cross-bedded bioclastic grainstones having poor fabric selective porosity owing to occluding carbonate cements. Interparticle porosity is present only in quartzarenitic sandstones where early cementation by authigenic chlorite clays prevents a later stage of porosity reduction by diagenetic quartz cementation. Interparticle porosity and secondary fracture porosity is best developed within structurally high areas where late stages of porosity reduction by diagenetic carbonate cementation are not present. Spiro test rates within the field are commonly very high (6-49 MMCFGD).

Pennsylvanian horizons in the area are thrusted and commonly imbricated as the result of Permian-Pennsylvanian (Ouachita) tectonism. Structural analysis demonstrates a positive relationship between ultimate recovery (production) and structural position within closed culminations of a complex regional thrust plate duplex system. South Hartshorne field is anomalous because it produces from a low relief thrust plate, indicating that depositional facies and diagenesis play key roles in reservoir quality.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)