Preparation And Application Of Temperature- And Saturated Salt-resistance Polymers As Filtrated And Viscosifying Additives For Water-based Drilling Fluid

With the exploration and development of oilfield shifts to deep formation, complex formation and offshore deepwater, it put a higher request for temperature-and salinity-resistance of drilling fluids. Unfortunately, viscosifier and filtration reducer, as the key additives to control the rheological and filtrated properties of water-based drilling fluids, have the weaknesses, respectively. Viscosifiers fail to satisfy requirements of temperature-resistance and salinity-resistance simultaneously; synthesized-polymer filtration reducers are mostly linear-chain, which lead to the mud system subsidcance easily and subsequently perpormance degradation under high temperature after aging or presence of high valent cations, therefore, they fail to serve drilling operation of complex formation.Combined with the subject of "Research on Deep Well Drilling Fluid and HTHP Cementing Technology under Complicated Formations" of the major projects of national science technology and the oil exploited project of Permit H in Chad of CNPC, based on the influence of high temperature and salt on water-based drilling fluid (WBD), and designed principle of molecule structure, a new microemulsion PADA as viscosifier and a new comb-like polymer CPASA as viscosifying and filtrated additive for WBD were prepared. They both possessed excellent properties under high temperature and saturated salt conditions. Generally, FTIR,1H-NMR, Laser Particle Analyzer, SEM, TEM, Ubbelohde viscometer and TGA were used to characterize structure and test properties. As a result, PADA and CPASA degraded at 350 ℃ and 400 ℃, respectively. The particle average diameter of PADA was around 76.5 nm, and the comb conformation of CPASA was confirmed by SEM pictures. PADA and CPASA both presented desirable viscosifying and filtration reducing properties in freshwater base mud, composite salt or saturated salt muds before and after thermal aging tests. Particularly, PADA showed better viscosifying performance over the existing domestic products and equal performance with foreign polymer viscosifying product when presented at 170 ℃ in saturated salt mud, it also had functions of filtrate reducers and coat stabilizers. According to the results of SEM, zeta potential and particle diameter data, PADA microemulsion could firmly be absorbed onto clay particle surface and strengthen the mud net structure, which obviously modify the size grading of particles in drilling fluid, filter cake quality and colloidal stability. Besides, thermostability and nano-sized particles could also contribute to viscosifying, absorbing and filtration reducting behaviors. While CPASA is a more ideal filtration reducer than foreign Driscal D when presented at 200 ℃ in saturated brine mud with desirable rheological control ability. The comb conformation of CPASA under high density brine and its preferable thermostability could contribute to protection of absorption and hydration groups to form a strong net structure with clay particles, shielding the effect of NaCl on zeta potential in an attempt to achieve the viscosifying and stabilizing system. PADA has been put into pilot and industrial production.By analyzing the engineering characteristics of well Mongo W-1 in Block H of Chad, low solid anti-collapse drilling fluid system with excellent comprehensive performance such as temperature-resistance, salt-resistance, bad soil pollution-resistance and good lubrication property, regarding PADA microemulsion as the key additive,This drilling fluid system has been successfully applied in well Mongo W-1, and achieved good economic benefits. Results of field test shows that the developed PADA microemulsion drilling fluid system is of a great value of application and dissemination.