The Nature Conservancy, one of the world’s wealthiest environmental organizations, is drawing fire from other enviros for venturing into particularly unlikely territory: oil refining. In 1995, Mobil Oil gave the Conservancy a 2,263-acre Texas oil field that is one of the world’s last-known breeding grounds for the highly endangered Attwater’s prairie chicken. Rather than shutting off the petroleum spigots, the conservancy drilled new natural gas wells and let cattle continue to graze on the land — and reaped about $5.2 million in royalties over the last seven years. The Nature Conservancy claims that careful management is allowing it to protect the prairie chicken while working the land to raise money for other conservation efforts. The Texas oilfield isn’t an exception; nearly half of all conservancy-owned land is grazed, logged, farmed, drilled, or otherwise worked, although money from these activities amounts to less than 1 percent of the group’s annual revenues. Some other environmental groups criticize the conservancy for compromising its mission and being in bed with industry.