Maria Elena Kusiak¹, Thomas A. Ryer², José G. Salinas¹
(1) Andina, S.A, Santa Cruz de la Sierra, Bolivia
(2) Schlumberger, Houston, TX

Abstract: Sequence stratigraphy and facies of Carboniferous glacio-eustatic reservoirs of the La Peña and Tundy fields, Chaco Basin, Bolivia

The La Peña and Tundy fields produce oil and gas from sandstones of the Carboniferous San Telmo and Escarpment formations. The fluvial "Bolivar sands" at the top of the Escarpment Formation are sealed by marine shale in the lower part of the San Telmo. The San Telmo and Escarpment formations are separated by a major unconformity that displays considerable erosional relief, descending southeastward toward Rio Grande Field. The "La Pena sands" are of both shallow-marine and fluvial origin. A high-stand shoreline sandstone produces in the southern part of the field. It was incised by a generally west- to southwest-trending valley system. The aggradational valley fill that accumulated on the subsequent rise of relative sea level is sand-rich and produces in the central and northern parts of the field. It constitutes the principal San Telmo reservoir in La Peña field. Following aggradation and filling of the valley system, the sea transgressed across the area from southwest to northeast. A shoreface sandstone unit, the "Tundy sand", records a brief phase of progradation during the overall transgression. Its landward edge is defined at Tundy Field, where the shoreface sandstone constitutes the single reservoir. The seaward-most sands of this unit are productive in the northern part of La Peña field and pinch out southwestward in the middle part of the field. A unit of marine shale in the uppermost part of the San Telmo Formation serves as the top seal for both the Tundy and La Peña sands.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana