Research On Rapid Decline In Wellhead Production Of Ordovician Reservoir In Tuofutai Area Of Tahe Oilfield

Oil wells production always decline along with continuous extraction of underground fluid, decreases gradually of remaining reserves and reservoir energy declining on stream. After ending a period of the plateau, it will enter the later stage of production decline. The characteristics of production declining are discrepant at different production stages. And based on this different decline characteristics oil wells are classified into four types: higher and stabilized production well, declined with low speed well, declined in medium speed well and declined rapidly well. In the actual development of Ordovician reservoir in Tuofutai area of Tahe oilfield, however, it happened an unusual problem that a part of oil wells suddenly declined rapidly even abnormal unflowing when production is relative high in production decline stages. This affects reservoir development in Tuofutai area by a large extent, so it needs a comprehensive analysis of the abnormal phenomenon in order to guiding oilfield development scientifically and reasonably.According to basic geological characteristics and development status of Ordovician carbonate reservoir in Tuofutai area, based on identification of reservoir space characteristics, combine with seism, drilling and well completion, well logging, dynamic monitoring, development performance and development measures, etc., reservoir types and characteristics, development performance characteristics and control factors of 9 declined rapidly wells are analyzed. And it mainly studied on the causes of rapid decline of wellhead production from formation energy, dissolved gas phase state, reservoir physical property, oil and water distribution, oil production system and the connectivity between wells, and then analyzed simply of control factors that affect oil wells production variation. Finally the countermeasures are put forward according to above-mentioned reasons for rapid decline of wellhead production. Finally it is concluded that the following points:(1) According to production and wellhead pressure characteristics of oil wells of the Ordovician reservoir in Tuofutai area during the process of natural flow, 9 representative wells that decline rapidly in wellhead production are divided into three types: stable and high production, pressure drops slowly; relatively high production that decline stably or slowly, pressure decline slowly or rapidly; unstable production that decline rapidly or batched, pressure decline rapidly, very short flow period. And the corresponding reservoir spaces of above three development performance characteristics are: Large vuggy unit with active bottom water; closed type small or medium-sized fractured cave; small fractured cave with high degree of filling.(2) There are five reasons of rapid decline in wellhead production in Tuofutai area oil wells by means of studying: energy exhaustion, crude oil deaeration, reservoir pollution, water cut rising, high rate of oil production.(3) According to the reasons of rapid decline in wellhead production, it also concludes a few factors which affect oil well production variation and the following several aspects: the geological factors are: types of reservoirs, karst-cave filling degree, formation energy, water cut increase, crude oil degassing degree, reservoir pollution levels; the engineering factors are: working system, oil production rate, production technology.Production of single well and unit is not always determined by a single factor, but the combined action of many factors. So it should research production variation under the different situation, in order to determine the adjustable measures reasonably.(4) It should put forward corresponding measures according to different reasons of rapid decline in wellhead production: i. The advice is water flooding before pressure dropped to a lower degree for energy shortage and crude oil deaeration in rapid decline in wellhead production, which in order to restore formation energy and keep well pressure; ii. It should offer the acid fracturing treatment for sudden drop production caused by reservoir production, which can improve flowing channels of the bottom hole and restore the seepage ability; iii. It can via adjusting and water injection periodically to change flow direction and pressure field, so as to change water to promote; or shut down high containing water wells, high sealing channeling and seal the well aquifer; water injection profile control and adjust the water flooding structure to prevent water cut rising; iv. It should reasonably control oil production rate for oil recovery rate caused by high output, which can make the oil well output smoothly so as to be flowing production for a long time.