Objective A key parameter necessary for estimating the amount of oil left in a reservoir after water displacement is the residual oil saturation (ROS). Since the most reliable values of ROS can be obtained only through field measurements, several methods, based upon log recording and tracer injection, have been proposed. Main aim of this project is testing and improving some of these methods in order :- to identify screening criteria for selecting the best ROS evaluation techniques(s) to be applied under different reservoir and/or well condition;- to compare on the same well the results obtained applying methods with various investigation depths.PHASE 1- A lab methodology for selecting and characterizing the tracers was developed.- The chemical tracers for SWTTs on selected sites were chosen and their partition coefficients at reservoir conditions were determined. It was observed that the partition coefficient strongly depends on oil composition, as well as the hydrolysis kinetics is strongly affected by the pH and by the mineralogical composition of the reservoir rock.- The radioactive tracers for GR-LIL and IWTT were selected by measuring their partition coefficients and their half time.- Computer codes designed for interpreting the field tests were developed. Two simulators, found in the technical literature, were improved by AGIP adding to their original code subroutines for graphic part and making them iterative. SMEA(P) in collaboration with IFP developed a two-dimensional simulator which takes into account fluid drift phenomenon.PHASE 2The wells chosen for the experiments were located in France (Chuelles field), Cameroun (Combo Center Marine field), Italy (Cortemaggiore and Torrente Tona fields).At the different sites the following techniques were applied :- CHUELLES. Conventional logging (GR, NL and C/O) on three wells; GR-LIL and PNC-LIL on one well. A SWTT was tried by injecting water with isotropyl formate and methanol. Two IWTTs were also run on injecting tritiated water and Nal in one case, and water with NAL, phenol and o-cresol in the other. The interpretation of the experimental data gave ROS values in fair agreement between them.- KOMBO. Conventional PNC and LIL-PNC were run in a gravel-packed well. The test confirmed the flexibility of LIL-PNC method, as well as its capability to give good indications of ROS when the mobility ratio is favourable.- CORTEMAGGIORE. Conventional logging (GR, PNC) and LIL-PNC in one well. A SWTT was also tried in the same well by injecting water with methyl acetate and ethyl alcohol. The interpretation of the experimental data of SWTT gave an average ROS value lower than those estimated through logging techniques. The discrepancy was probably caused by the high heterogeneity of the reservoir rock.- TORRENTE TONA. Conventional logging (GR, PNC,C/O) and LIL-PNC in one well. During the operations carried out for LIL-PNC a poor cement bond was discovered behind the casing covering the formation to be tested. The experiment was suspended and the planned SWTT cancelled.The project consists of two main phases :PHASE 1 - Preliminary studies, laboratory activities and development of computer codes.After an extensive survey of technical literature on this subject, an analysis of the reservoirs operated by SNEA(P) and AGIP should allow to find out the wells where the experiments can be run under the best operational conditions.The lab activity aims at setting up an experimental methodology for a quick selection and characterization of the most suitable tracers (chemical or radioactive) for each field where the ROS measurements are to be carried out. Both commercial products and new chemicals will be tested.The modelling activity is intended to develop computer programs and to adapt existing software packages for the interpretation of the field experiments.PHASE 2 - Preparation, execution and interpretation of the field tests.In the selected well sites, after the installation of required facilities, the following techniques will be tested :a) LOGGING. Recording of Gamma Ray (GR), Neutron Log (NL) and Carbon/oxygen (C/O) performed before and after the well perforation, if possible.b) LOG-INJECT-LOG (PNC-LIL). Recording of PNC log before and after the injection of a small slug of water at contrasting salinity with the formation brine.c) LOG-INJECT-LOG (GR-LIL). Recording of GR after the injection of a small slug of water doped with a radioactive compound.d) SINGLE-WELL TRACER TEST (SWTT). The technique consists of injecting a sufficiently large volume of water containing a primary tracer and an alcohol added for material balance control. After a convenient shut-in period to permit the tracer decomposition, the well is back-produced and the water is sampled for lab analysis.e) INTERWELL TRACER TEST (IWTT). The technique consists of injecting a slug of water doped with a radioactive agent and/or chemical tracers. The slug is pushed towards the producer wells where the water is sampled for lab analysis. Programme(s) ENG-HYDROCARB 2C - Programme (EEC) of support for technological development in the hydrocarbons sector, 1986-1989 Topic(s) 1.9 - PRODUCTION SYSTEMS Call for proposal Data not available Funding Scheme DEM - Demonstration contracts Coordinator GERTH EU contribution No data Address 232 AV. NAPOLEON BONAPARTE 92500 Rueil Malmaison France See on map Total cost No data
