The Use of Drilling Solid Waste as Amendment of Acid-Sulphate Soils of the Orinoco Delta
Authors: Vasquez P. , Urich J. , Gonzalez V. , Silva P. , Rodriguez A. 
Published: December 2007

The Venezuelan oil industry has begun an exploration and drilling program in the Orinoco Delta, and an intensive research is executed about the feasibility of landspreading as an option to dispose water based drilling wastes (DW) to avoid the contamination of water bodies. The original fluvial marine seasonal floodplain nearby Boca de Uracoa town (9 N, 62, 21' W), was modified after the closure of Manamo distributary, which led to the transformation of the original substrate with high pyrite contain, to acid-sulphate soils. Greenhouse experiments were carried out applying Drilling Waste (DW) equivalent doses of 0, 200, 500, 1000 and 1500 m3/ha to an acid-sulphate soil, using as test plant Zea mays var. PB-8. The results show that the elevated pH of DW (pH of 9.7) neutralizes the very acidic reaction of the acid-sulphate soils (pH 2.85) which is reflected on the higher production of biomass obtained with DW equivalent doses over 500 m3/ha. The Ba content in aerial biomass was below 0.2 g/g in all treatments, while Pb and Zn content were depleted by the parallel application of Phosphoric rock (PR). Concentrations of these elements in the soil equilibrium solution, shows very low leaching and low availability for vegetation.

Introduction

Development of the oil resources occurring in the tropical swamp forests in Eastern Venezuela in the states of Monagas, Delta Amacuro and Sucre, convey significant environmental challenges for the Venezuelan Oil Industry as well as for its business associates. One of these is related to the future disposal of water based Drilling Waste (DW) made up by cuttings and spent mud components under the following constraints:The absence in this region of consolidated soils were mud pit disposal can be performed,Corporate Environmental Policy that mandates the development of this resources in a cost effective environmentally surgical (minimal impact) way, andThe evolution of environmental regulations that moves towards banning the conventional mud pit disposal methods.

There constraints suggest that DW disposal should be dealt within the land reclamation frameworks. In order to proceed with this scheme, two premises are relevant. On one hand DW must be sought as a soil amendment analyzable with soil chemistry and fertility criteria. On the other hand, there are suitable soils (acid-sulphate pH &lt; 3.5), within cost effective distances that could function as harmless stable sinks for disposal of DW (basic, pH &gt;9.0).

In order to determine the feasibility of developing a safe landspreading technique for DW, that without harming vegetation growth can involve physical-chemical properties of acid-sulphate soils, a project that includes greenhouse, laboratory and field experiments leading to an operational scale landspreading procedure has been established. Preliminary laboratory results are reported in this paper.

Given the above premises, the location, occurrence and relevant properties of acidic and acid sulfate soils of Eastern Monagas and Delta Amacuro state, follows.

Description of landscape and soil processes The study area (Fig. 1), that has been chosen for the potential disposal of DW, is located Northeast of the town of Boca de Uracoa, in Monagas state (9 N, 62 21' W).

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