A PREVIOUS STUDY OF HUALLAGA BASIN. The Huallaga basin was not seriously explored until the early 1990’s when Mobil signed four concessions totaling 36,000 km2, covering almost the entire basin. Mobil acquired the first seismic shot in the basin and through three seismic campaigns, recorded a total 1600 km of data. After drilling the Ponasillo 1 X in 1992, which was plugged and abandoned as a dry hole, Mobil relinquished their acreage in 1993. The Huallaga Basin has largely remained dormant from an exploration viewpoint since that time.
The fold and thrust belt separating the Huallaga from the Marañon Basin was first seriously explored in 1996 with the signing of Block 72 by Occidental Peruana. In the process of evaluating the Block, Occidental reprocessed 615 km of seismic data in the Huallaga area and acquired 148 km more. Occidental relinquished the area in 1999 without drilling a well.
In 2000, Advantage Resources signed Block 87, which has a configuration similar to that of the old Occidental Block. As of this writing, Advantage with their partners Burlington Resources, had completed extensive geological fieldwork in the Huallaga Area reprocessed 409 km of Mobil and Occidental seismic data and acquired an additional 201 km of seismic data. This recent seismic data acquisition was not interpreted as part of this study.
The southwestern Marañon and northwestern Ucayali Basins bordering the Huallaga fold and thrust belt, have been the recipients of considerable more activity in years past. The first significant exploration in southwestern Marañon was done by Texaco in the 1950’s whose work culminated with the drilling of the Yurimaguas 1X well. Exploration returned to the area in the late 1970’s with Deminex in Block 12. In the process of their evaluation, Deminex acquired 2890 km of seismic data and drilled two wells, Loreto 1X, and Shanusi 1X, the later of which had significant gas shows in the Pucará Formation. Since the departure of Deminex in 1970’s, only minimal work has been done in the area. Another activity was a one line seismic acquisition by Coastal Petroleum in 1998 that was shot to confirm the northwest closure of the Yurimaguas structure. This acquisition was part of Coastal’s much larger exploration activity that was focused primarily on the area surrounding the Contaya Arch and the northern Ucayali Basin when they controlled Blocks 73 and 74 between 1994 and 1999. During this time Coastal reprocessed 2890 km of seismic data, acquired 380 km in 1995 and 261 km in 1998. Before relinquishing their blocks, Coastal drilled three wells, Orellana 1X, Santa Catalina 1X and Insaya 1X. All three wells were plugged and abandoned.
The Huallaga Basin for all intensive purposes is considered a tectonic basin formed by Andean compressional deformation during the Late Tertiary prior to which it represented the western reaches of the greater Marañon basin. The present day Basin is 400
km long from north to south with a maximum width of 100 km. A large linear regional structurally complex uplift separates the Jurassic-Tertiary sequence of the Huallaga basin from the equivalent section in the Marañon basin. This frontal belt is a complex product of inversion, thrust and/or salt tectonics on which rocks as old as Triassic are exposed. The youngest rocks flanking the uplift are Neogene in age. Similar to the western Marañon basin, the Lower Cretaceous beds of the Huallaga rest directly upon a pre-Cretaceous Mesozoic section that includes Jurassic–Triassic carbonates and evaporites, which in turn overlies an unknown but presumably Paleozoic stratified sedimentary section.
The geological evolution of the study area is controlled by two regional tectonic systems recognized in the sub-Andean basins of Peru. The first, the pre-Andean System, encompasses three cycles of Ordovician, Devonian and Permo-Carboniferous ages overlying the Precambrian basement of the Guyana and Brazilian Shields. The second, the Andean System, was initiated with the beginning of subduction along the western margin of Peru. It encompasses several mega-stratigraphic sequences and numerous minor sedimentary cycles, ranging from late Permian to the Present.