ABSTRACT: Porosity and Permeability in Phylloid Algal Buildup, Nena Lucia #112, Nena Lucia Field, Nolan County, Texas
LOCKLIN, JO ANN, Texaco Exploration and Production Technology Department, Houston, TX
Examination of Middle Pennsylvanian (Desmoinesian) core from the Nena Lucia #112 well reveals limestone facies associated with phylloid algal buildups. The facies include crinoidal, pelletal-foraminiferal, algal-plate, algal-intraclast, and terrigenous siliciclastics.
Comparison of the core with well logs and measured core porosity and permeability data indicates that the best continuous porosity and permeability are associated with the algalplate facies (porosity to 20 %, permeability exceeding 400 md). Petrographic examination of thin sections taken from the core shows that porosity is mainly secondary. The original algal plates, outlined by micrite envelopes, have been leached and partially filled by equant calcite. Shelter porosity, occurring beneath the algal plates, and open fractures, also contribute to total porosity.
Moldic and fracture porosity are also dominant in the pelletal-foraminiferal and algal intraclast facies. However, continuous porosity and permeability are considerably lower in these facies (porosity less than 10 %, permeability less than 5 md). The crinoidal and terrigenous siliciclastic facies are generally nonporous.
AAPG Search and Discovery Article #91018©1992 AAPG Southwest Section Meeting, Midland, Texas, April 21-24, 1992 (2009)